Schedule SMS Reminders with Sinch in RedwoodJS: Complete Implementation Guide

Build a RedwoodJS application that schedules and sends SMS reminders using the Sinch SMS API. Create an appointment reminder system where users enter appointment details and the application automatically schedules an SMS reminder via Sinch at a specified time before the appointment.

This guide solves the common need for automated, time-sensitive notifications without requiring complex background job infrastructure. Instead, leverage Sinch's built-in send_at scheduling capabilities to handle the job scheduling for you.

Real-world applications:

• Medical practices reducing no-shows by 30-40% with timely appointment reminders
• Service businesses (salons, auto repair, consulting) improving customer experience with automated confirmations
• SaaS platforms sending trial expiration warnings and subscription renewal notices
• Educational institutions managing class schedules and exam notifications

Key Technologies:

• RedwoodJS: A full-stack, serverless-friendly JavaScript/TypeScript framework for the web. Chosen for its integrated frontend (React) and backend (GraphQL API, Prisma), developer experience, and conventions.
• Sinch SMS API: A service for sending and receiving SMS messages globally. Use its Node.js SDK and specifically its send_at feature for scheduling.
• Prisma: A next-generation ORM for Node.js and TypeScript, used by RedwoodJS for database access.
• Node.js: The underlying JavaScript runtime environment.
• PostgreSQL (or SQLite): The database for storing appointment information.

System Architecture:

Data flow:

1. User interacts with the RedwoodJS Frontend (React) in their browser.
2. Frontend sends requests to the RedwoodJS API (GraphQL).
3. API routes requests to the Redwood Reminder Service.
4. Reminder Service uses Prisma ORM to store and retrieve data from the Database (PostgreSQL/SQLite).
5. Reminder Service makes API calls to the Sinch SMS API to schedule messages.
6. At the scheduled time, the Sinch SMS API sends the SMS to the User's Phone.

Prerequisites:

• Node.js (v20 or higher recommended – check RedwoodJS docs for current requirements)
• Yarn v1 (v1.22.x or higher recommended; RedwoodJS currently relies on Yarn v1 features)
• A Sinch Account: API credentials (Project ID, Key ID, Key Secret) and a provisioned phone number
• Access to a terminal or command prompt
• Basic understanding of JavaScript, React, GraphQL, and databases

Obtaining Sinch credentials:

1. Sign up at sinch.com and create a free account
2. Navigate to your Dashboard → Projects → Create New Project
3. Go to API Credentials section and generate Key ID and Key Secret (save these securely)
4. Navigate to Numbers → Buy Numbers → Select your region and purchase an SMS-capable number
5. Verify your number is assigned to your Project ID in the Numbers dashboard

Sinch API Scheduling Requirements:

Regional Endpoints:

Sinch API Error Codes:

Source: Sinch SMS Batches API Documentation

Final Outcome:

A RedwoodJS application with a simple UI to schedule appointment reminders. The backend validates input, stores appointment details, and uses the Sinch Node SDK to schedule an SMS to be sent 2 hours before the scheduled appointment time.

How Do You Set Up a RedwoodJS Project for SMS Scheduling?

Initialize a new RedwoodJS project and configure the necessary environment.

1. Create Redwood App: Open your terminal and navigate to the directory where you want to create your project. Run the following command, replacing <your-app-name> with your desired project name (e.g., redwood-sinch-reminders):

   bashCopy

   yarn create redwood-app <your-app-name> --typescript

   • Use --typescript for enhanced type safety, recommended for production applications.
   • Follow the prompts:
     • Initialize git repo? yes (recommended)
     • Enter commit message: Initial commit (or your preferred message)
     • Run yarn install? yes

2. Navigate to Project Directory:

   bashCopy

   cd <your-app-name>

3. Install Additional Dependencies: Install the Sinch SDK and luxon for robust date/time manipulation.

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   yarn workspace api add @sinch/sdk-core luxon
   yarn workspace api add -D @types/luxon # Dev dependency for types

   • @sinch/sdk-core: The official Sinch Node.js SDK.
   • luxon: A powerful library for handling dates, times, and time zones.

Why Luxon over native Date or other libraries?

Luxon provides:

• Immutability: Unlike native Date, Luxon DateTime objects don't mutate, preventing bugs
• Time zone support: First-class IANA time zone handling (e.g., America/New_York)
• ISO-8601 formatting: Built-in .toISO() method matches Sinch API requirements exactly
• Readable API: appointmentDateTime.minus({ hours: 2 }) vs. complex Date arithmetic

Alternative libraries like Moment.js are deprecated, and Day.js lacks robust time zone support without plugins.

4. Environment Variable Setup: Redwood uses .env files for environment variables. The Sinch SDK requires credentials. Create a .env file in the root of your project:

   bashCopy

   touch .env

   Add the following variables to your .env file, replacing the placeholder values with your actual Sinch credentials and configuration:

   dotenvCopy

   # .env
   # Find these in your Sinch Dashboard. Navigate to API Credentials
   # under your Project Settings (often via Access Keys section).
   SINCH_KEY_ID='YOUR_SINCH_KEY_ID'
   SINCH_KEY_SECRET='YOUR_SINCH_KEY_SECRET'
   SINCH_PROJECT_ID='YOUR_SINCH_PROJECT_ID'
   
   # Obtain from your Sinch Customer Dashboard -> Numbers -> Your Numbers
   # Ensure the number is SMS enabled and assigned to the correct Project ID
   SINCH_FROM_NUMBER='+1xxxxxxxxxx' # Use E.164 format
   
   # Specify the Sinch API region (e.g., 'us' or 'eu')
   # Regional endpoints: us.sms.api.sinch.com (US), eu.sms.api.sinch.com (EU),
   # au.sms.api.sinch.com (AU), br.sms.api.sinch.com (BR), ca.sms.api.sinch.com (CA)
   # Choose the region closest to your user base for optimal performance.
   SINCH_SMS_REGION='us'
   
   # Default country code prefix for numbers if not provided in E.164 format
   # Adjust based on your primary target region if needed, but prefer E.164 input
   DEFAULT_COUNTRY_CODE='+1'

   • SINCH_KEY_ID, SINCH_KEY_SECRET, SINCH_PROJECT_ID: Find these in your Sinch Dashboard under your project's API credentials/Access Keys section. Treat SINCH_KEY_SECRET like a password – never commit it to Git.
   • SINCH_FROM_NUMBER: A virtual number you've acquired through Sinch, enabled for SMS, and associated with your Project ID. Must be in E.164 format (e.g., +12025550187).
   • SINCH_SMS_REGION: The regional endpoint for the Sinch API. Available regions: us (United States), eu (European Union), au (Australia), br (Brazil), ca (Canada). Use the region closest to your user base or where your account is homed.
   • DEFAULT_COUNTRY_CODE: Used as a fallback if the user enters a local number format. Best practice requires E.164 format input.

Source: Sinch SMS API Reference – Regional Endpoints

5. Add .env to .gitignore: Ensure your .env file (containing secrets) is not committed to version control. Open your project's root .gitignore file and add .env if it's not already present.

   textCopy

   # .gitignore
   # ... other entries
   .env
   .env.defaults # Often safe to commit, but double-check
   .env.development
   .env.production
   # ...

6. Initial Commit (if not done during creation): If you didn't initialize Git during create redwood-app:

   bashCopy

   git init
   git add .
   git commit -m "Initial project setup with dependencies and env structure"

How Do You Create the Database Schema for Reminder Scheduling?

Define a database table to store the details of scheduled reminders.

1. Define Prisma Schema: Open api/db/schema.prisma and define a model for Reminder:

   prismaCopy

   // api/db/schema.prisma
   
   datasource db {
     provider = "postgresql" // Or "sqlite" for local dev/simplicity
     url      = env("DATABASE_URL")
   }
   
   generator client {
     provider      = "prisma-client-js"
     binaryTargets = "native"
   }
   
   model Reminder {
     id              Int      @id @default(autoincrement())
     patientName     String
     doctorName      String
     phoneNumber     String   // Store in E.164 format (e.g., +1xxxxxxxxxx)
     appointmentTime DateTime // Store in UTC
     reminderTime    DateTime // Store in UTC (when the SMS should be sent)
     status          String   @default("PENDING") // PENDING, SENT, FAILED
     sinchBatchId    String?  // Store the ID returned by Sinch API
     createdAt       DateTime @default(now())
     updatedAt       DateTime @updatedAt
   
     @@index([status, reminderTime]) // Index for potential future querying/cleanup
   }

   • Store phone numbers in E.164 format for consistency.
   • Store all DateTime fields in UTC to avoid time zone issues.
   • status tracks the state of the reminder (PENDING means scheduled but not yet sent).
   • sinchBatchId can be useful for tracking the message status within Sinch later.
   • An index on status and reminderTime could be useful for querying pending jobs or cleanup tasks.

Status lifecycle and state transitions:

• PENDING: Reminder scheduled with Sinch, awaiting send time
• SENT: Sinch confirmed message delivery (requires webhook integration)
• FAILED: Scheduling or delivery failed (check sinchBatchId in Sinch dashboard for details)

Enhanced schema for production:

model Reminder {
  id              Int      @id @default(autoincrement())
  patientName     String
  doctorName      String
  phoneNumber     String
  appointmentTime DateTime
  reminderTime    DateTime
  status          String   @default("PENDING")
  sinchBatchId    String?
  retryCount      Int      @default(0) // Track retry attempts
  errorMessage    String?  // Store last error for debugging
  deliveryStatus  String?  // DELIVERED, UNDELIVERED, EXPIRED from webhook
  createdAt       DateTime @default(now())
  updatedAt       DateTime @updatedAt

  @@index([status, reminderTime])
}

2. Set up Database Connection: Ensure your DATABASE_URL in the .env file points to your database (e.g., postgresql://user:password@host:port/database). For local development, Redwood defaults to SQLite, which requires no extra setup if you stick with the default provider = "sqlite".

Troubleshooting database connection issues:

3. Run Database Migration: Apply the schema changes to your database:

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   yarn rw prisma migrate dev

   • This command creates a new SQL migration file based on your schema.prisma changes and applies it to your development database. Provide a name for the migration when prompted (e.g., create reminder model).

How Do You Implement the Sinch SMS Scheduling Service in RedwoodJS?

Create the RedwoodJS service that handles the logic for scheduling reminders.

1. Generate Service Files: Use the Redwood generator to create the necessary service and GraphQL files:

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   yarn rw g service reminder

   This creates:

   • api/src/services/reminders/reminders.ts (Service logic)
   • api/src/services/reminders/reminders.scenarios.ts (Seed data for testing)
   • api/src/services/reminders/reminders.test.ts (Unit tests)
   • api/src/graphql/reminders.sdl.ts (GraphQL schema definition)

2. Implement the scheduleReminder Service Function: Open api/src/services/reminders/reminders.ts and add the logic to create a reminder record and schedule the SMS via Sinch.

   typescriptCopy

   // api/src/services/reminders/reminders.ts
   import { validate } from '@redwoodjs/api'
   import type { MutationResolvers } from 'types/graphql'
   
   import { db } from 'src/lib/db'
   import { logger } from 'src/lib/logger'
   import { sinchClient } from 'src/lib/sinch' // We'll create this client lib next
   import { DateTime } from 'luxon'
   
   interface ScheduleReminderInput {
     patientName: string
     doctorName: string
     phoneNumber: string // Expecting E.164 format
     appointmentDate: string // e.g., '2025-07-15'
     appointmentTime: string // e.g., '14:30'
     timeZone: string // e.g., 'America/New_York'
   }
   
   // --- Helper Function for Phone Number Validation/Normalization ---
   const normalizePhoneNumber = (inputPhone: string): string => {
     // Basic check for E.164 format (starts with +, followed by digits)
     if (/^\+[1-9]\d{1,14}$/.test(inputPhone)) {
       return inputPhone
     }
     // Attempt to prefix with default country code if it looks like a local number
     // WARNING: This is a significant simplification. Real-world validation is complex.
     // Using a library like libphonenumber-js is highly recommended for production
     // as it handles varying international and local formats, plus provides
     // robust validation, which this basic example lacks.
     const digits = inputPhone.replace(/\D/g, '')
     if (digits.length >= 10) { // Basic check for common lengths
       return (process.env.DEFAULT_COUNTRY_CODE || '+1') + digits
     }
     throw new Error('Invalid phone number format. Use E.164 format (e.g., +1xxxxxxxxxx).')
   }
   
   // --- Main Service Function ---
   export const scheduleReminder: MutationResolvers['scheduleReminder'] = async ({
     input,
   }: {
     input: ScheduleReminderInput
   }) => {
     logger.info({ input }, 'Received request to schedule reminder')
   
     // 1. Validate Input
     validate(input.patientName, 'Patient Name', { presence: true, length: { min: 1 } })
     validate(input.doctorName, 'Doctor Name', { presence: true, length: { min: 1 } })
     validate(input.phoneNumber, 'Phone Number', { presence: true })
     validate(input.appointmentDate, 'Appointment Date', { presence: true })
     validate(input.appointmentTime, 'Appointment Time', { presence: true })
     validate(input.timeZone, 'Time Zone', { presence: true }) // Ensure timezone is provided
   
     let normalizedPhone: string;
     try {
       normalizedPhone = normalizePhoneNumber(input.phoneNumber)
     } catch (error) {
       logger.error({ error }, 'Phone number validation failed')
       throw new Error(error.message)
     }
   
     // 2. Calculate Appointment and Reminder Times using Luxon
     let appointmentDateTime: DateTime;
     let reminderDateTime: DateTime;
     try {
       const dateTimeString = `${input.appointmentDate}T${input.appointmentTime}`
       appointmentDateTime = DateTime.fromISO(dateTimeString, { zone: input.timeZone })
   
       if (!appointmentDateTime.isValid) {
         throw new Error(`Invalid date/time format or timezone: ${appointmentDateTime.invalidReason}`)
       }
   
       // Calculate reminder time (e.g., 2 hours before appointment)
       reminderDateTime = appointmentDateTime.minus({ hours: 2 })
   
       // Validation: Ensure reminder time is in the future
       if (reminderDateTime <= DateTime.now()) {
         throw new Error('Calculated reminder time is in the past. Appointment must be sufficiently in the future.')
       }
   
     } catch (error) {
        logger.error({ error, input }, 'Error processing date/time')
        throw new Error(`Failed to process date/time: ${error.message}`)
     }
   
     // Convert times to UTC for storage and Sinch API
     const appointmentTimeUtc = appointmentDateTime.toUTC()
     const reminderTimeUtc = reminderDateTime.toUTC()
   
     // Format for Sinch API (ISO 8601 with Z for UTC)
     const sendAtIso = reminderTimeUtc.toISO() // Luxon defaults to ISO 8601
   
     // 3. Construct SMS Message Body
     const messageBody = `Hi ${input.patientName}, this is a reminder for your appointment with Dr. ${input.doctorName} on ${appointmentDateTime.toLocaleString(DateTime.DATE_MED_WITH_WEEKDAY)} at ${appointmentDateTime.toLocaleString(DateTime.TIME_SIMPLE)}. Reply STOP to unsubscribe.` // Added opt-out language
   
     logger.info({
         normalizedPhone,
         messageBody,
         sendAtIso,
         appointmentTime: appointmentDateTime.toISO(),
         timeZone: input.timeZone
       }, 'Prepared reminder details')
   
     // 4. Schedule SMS with Sinch API
     let sinchResponse;
     try {
       sinchResponse = await sinchClient.sms.batches.send({
         sendSMSRequestBody: {
           to: [normalizedPhone],
           from: process.env.SINCH_FROM_NUMBER,
           body: messageBody,
           send_at: sendAtIso, // Use the calculated UTC time
           // Optional: Add delivery_report: 'full' or 'summary' if needed
         },
       })
       logger.info({ sinchResponse }, 'Successfully scheduled SMS via Sinch')
     } catch (error) {
       logger.error({ error }, 'Failed to schedule SMS via Sinch API')
       // Consider creating the DB record with status 'FAILED' or throwing
       throw new Error(`Failed to schedule SMS: ${error.response?.data?.error?.message || error.message}`)
     }
   
     // 5. Store Reminder in Database
     try {
       const createdReminder = await db.reminder.create({
         data: {
           patientName: input.patientName,
           doctorName: input.doctorName,
           phoneNumber: normalizedPhone,
           appointmentTime: appointmentTimeUtc.toJSDate(), // Convert Luxon DateTime to JS Date for Prisma
           reminderTime: reminderTimeUtc.toJSDate(),
           status: 'PENDING', // Indicates scheduled but not yet sent
           sinchBatchId: sinchResponse?.id, // Store the batch ID if available
         },
       })
       logger.info({ reminderId: createdReminder.id }, 'Reminder record created in database')
       return createdReminder
     } catch (dbError) {
       logger.error({ dbError, sinchBatchId: sinchResponse?.id }, 'Failed to save reminder to database after scheduling SMS')
       // Critical failure: SMS scheduled, but DB save failed.
       // Production systems need robust compensation logic: e.g., save reminder
       // with 'SCHEDULING_FAILED_DB' status *before* API call, update to
       // 'PENDING' after success, or have a cleanup job identify orphaned scheduled
       // messages via the Sinch Batch ID. Log details for manual intervention.
       // Consider attempting to cancel the Sinch message if the API supports it.
       throw new Error('Failed to save reminder details after scheduling. Manual check required.')
     }
   }

   • Input Validation: Uses Redwood's validate and custom logic for the phone number and date/time. The phone number normalization explicitly notes its limitations and recommends libphonenumber-js for production.
   • Date/Time Handling: Leverages luxon to parse the input date/time with the provided time zone, calculate the reminder time, and convert both to UTC for storage and the API call. Validates that the reminder time is in the future.
   • Sinch Client: Calls the sinchClient.sms.batches.send method (you'll define sinchClient next).
   • send_at Parameter: Passes the calculated reminderTimeUtc in ISO-8601 format to Sinch's send_at parameter. Maximum scheduling window: 3 days (Sinch default expire_at).
   • Database Storage: Saves the reminder details with status 'PENDING' and the sinchBatchId.
   • Error Handling: Includes try...catch blocks. The database error handling after a successful Sinch call includes warnings and suggestions for compensation logic.

Transaction handling and idempotency:

The current implementation has a race condition: if the SMS schedules successfully but the database write fails, you have an orphaned scheduled message. Production systems should:

1. Save first, update later: Create DB record with status PENDING_SCHEDULE before calling Sinch, then update to PENDING after success
2. Use transactions: Wrap both operations in a database transaction (note: external API calls can't be rolled back)
3. Implement idempotency: Store a unique request ID to prevent duplicate scheduling on retry

Canceling scheduled messages:

Add this function to handle cancellations:

export const cancelReminder: MutationResolvers['cancelReminder'] = async ({ id }) => {
  const reminder = await db.reminder.findUnique({ where: { id } })

  if (!reminder) throw new Error('Reminder not found')
  if (reminder.status !== 'PENDING') throw new Error('Can only cancel pending reminders')

  try {
    // Cancel via Sinch API
    await sinchClient.sms.batches.cancel(reminder.sinchBatchId)

    // Update database
    return await db.reminder.update({
      where: { id },
      data: { status: 'CANCELLED' }
    })
  } catch (error) {
    logger.error({ error, reminderId: id }, 'Failed to cancel reminder')
    throw new Error(`Cancellation failed: ${error.message}`)
  }
}

Source: Sinch SMS Batches API – send_at Parameter

3. Create Sinch Client Library: Centralize the Sinch SDK client initialization.

   Create a new file: api/src/lib/sinch.ts

   typescriptCopy

   // api/src/lib/sinch.ts
   import { SinchClient } from '@sinch/sdk-core'
   import { logger } from './logger'
   
   // Ensure required environment variables are present
   const requiredEnvVars: string[] = [
     'SINCH_PROJECT_ID',
     'SINCH_KEY_ID',
     'SINCH_KEY_SECRET',
     'SINCH_SMS_REGION', // Crucial for API endpoint routing
     'SINCH_FROM_NUMBER', // Needed for sending
   ]
   
   for (const envVar of requiredEnvVars) {
     if (!process.env[envVar]) {
       const errorMessage = `Configuration error: Missing required Sinch environment variable ${envVar}`
       logger.fatal(errorMessage)
       // Throwing here will prevent the app from starting without essential config
       throw new Error(errorMessage)
     }
   }
   
   // Initialize the Sinch Client
   // The SDK should ideally use the provided credentials and potentially region
   // information to route requests correctly.
   export const sinchClient = new SinchClient({
     projectId: process.env.SINCH_PROJECT_ID,
     keyId: process.env.SINCH_KEY_ID,
     keySecret: process.env.SINCH_KEY_SECRET,
     // The @sinch/sdk-core might use the region in different ways depending on the specific API (SMS, Voice etc.)
     // Ensure SINCH_SMS_REGION is set correctly in your environment.
     // Consult the latest Sinch Node.js SDK documentation for the precise method
     // of ensuring the SMS API calls target the correct region if issues arise.
     // It might involve setting a base URL or a specific regional property.
   })
   
   
   // Log confirmation that the client is initialized (without exposing secrets)
   logger.info('Sinch Client Initialized with Project ID and Key ID.')
   
   // Although the region variable is checked above, re-emphasize its importance.
   logger.info(`Sinch client configured to target region: ${process.env.SINCH_SMS_REGION}`)

   • This initializes the SinchClient using the environment variables.
   • Includes strict checks to ensure necessary variables are set, preventing runtime errors due to missing configuration.
   • Exports the initialized client for use in services.
   • Clarifies the importance of the SINCH_SMS_REGION environment variable for correct API endpoint targeting and advises checking Sinch SDK docs for the specific mechanism if needed.

Configuring regional endpoints:

If the SDK doesn't automatically route based on SINCH_SMS_REGION, configure the base URL explicitly:

const regionEndpoints = {
  us: 'https://us.sms.api.sinch.com',
  eu: 'https://eu.sms.api.sinch.com',
  au: 'https://au.sms.api.sinch.com',
  br: 'https://br.sms.api.sinch.com',
  ca: 'https://ca.sms.api.sinch.com',
}

export const sinchClient = new SinchClient({
  projectId: process.env.SINCH_PROJECT_ID,
  keyId: process.env.SINCH_KEY_ID,
  keySecret: process.env.SINCH_KEY_SECRET,
  smsServicePlanId: process.env.SINCH_PROJECT_ID,
  smsRegion: process.env.SINCH_SMS_REGION,
  // If SDK supports custom base URL:
  // baseUrl: regionEndpoints[process.env.SINCH_SMS_REGION]
})

Check the @sinch/sdk-core documentation for the exact initialization parameters.

How Do You Build the GraphQL API for SMS Reminders?

Define the GraphQL mutation to expose the scheduleReminder service function.

1. Define GraphQL Schema: Open api/src/graphql/reminders.sdl.ts. Redwood generators created a basic structure. Modify it to define the ScheduleReminderInput and the scheduleReminder mutation.

   graphqlCopy

   # api/src/graphql/reminders.sdl.ts
   
   input ScheduleReminderInput {
     patientName: String!
     doctorName: String!
     phoneNumber: String! # E.164 format preferred (e.g., +1xxxxxxxxxx)
     appointmentDate: String! # Format: YYYY-MM-DD
     appointmentTime: String! # Format: HH:MM (24-hour)
     timeZone: String!      # IANA Time Zone Name (e.g., America/New_York)
   }
   
   type Reminder {
     id: Int!
     patientName: String!
     doctorName: String!
     phoneNumber: String!
     appointmentTime: DateTime!
     reminderTime: DateTime!
     status: String!
     sinchBatchId: String
     createdAt: DateTime!
     updatedAt: DateTime!
   }
   
   type Mutation {
     """Schedules a new SMS reminder via Sinch."""
     scheduleReminder(input: ScheduleReminderInput!): Reminder # @requireAuth removed for initial dev
     """Cancels a pending SMS reminder."""
     cancelReminder(id: Int!): Reminder
   }
   
   type Query {
     """Retrieves all reminders for the authenticated user."""
     reminders: [Reminder!]! @requireAuth
     """Retrieves a single reminder by ID."""
     reminder(id: Int!): Reminder @requireAuth
   }

   • Defines the input structure expected by the mutation. Using ! marks fields as required.
   • Defines the Reminder type that mirrors our Prisma model and will be returned by the mutation on success.
   • Defines the scheduleReminder mutation, taking the input and returning a Reminder.
   • @requireAuth: Initially added by the generator. It has been removed here for easier initial testing. Important: Removing authentication is only for initial development convenience. You MUST re-enable or implement proper authentication before deploying to any non-local environment.

2. Testing the API Endpoint: Once the development server is running (yarn rw dev), test the mutation using the Redwood GraphQL Playground (usually at http://localhost:8911/graphql) or a tool like curl or Postman.

   GraphQL Playground Mutation:

   graphqlCopy

   mutation ScheduleNewReminder {
     scheduleReminder(
       input: {
         patientName: "Alice Wonderland"
         doctorName: "Cheshire"
         phoneNumber: "+15551234567" # Use a real test number if possible
         appointmentDate: "2025-08-22" # Ensure this date/time is far enough in the future
         appointmentTime: "15:00"
         timeZone: "America/Los_Angeles" # Use a valid IANA timezone
       }
     ) {
       id
       patientName
       phoneNumber
       appointmentTime
       reminderTime
       status
       sinchBatchId
     }
   }

   Expected Response:

   jsonCopy

   {
     "data": {
       "scheduleReminder": {
         "id": 1,
         "patientName": "Alice Wonderland",
         "phoneNumber": "+15551234567",
         "appointmentTime": "2025-08-22T22:00:00.000Z",
         "reminderTime": "2025-08-22T20:00:00.000Z",
         "status": "PENDING",
         "sinchBatchId": "01HXYZ123ABC..."
       }
     }
   }

   Common Errors:

   Error Message	Cause	Solution
   Invalid phone number format	Phone not in E.164	Add + and country code
   Calculated reminder time is in the past	Appointment too soon	Schedule at least 2+ hours ahead
   Failed to schedule SMS: 40101	Invalid Sinch credentials	Verify Key ID/Secret in .env
   Database error: unique constraint	Duplicate submission	Implement idempotency with request IDs

   Debugging Tips:

   1. Check API server logs in terminal running yarn rw dev
   2. Verify Sinch Dashboard → Logs → API Logs for request details
   3. Use GraphQL Playground's "DOCS" tab to explore schema
   4. Enable verbose logging: logger.debug({ sinchResponse }, 'Full response') in service
   5. Test with curl to isolate frontend issues:

   Curl Example:

   bashCopy

   curl 'http://localhost:8911/graphql' \
     -H 'Content-Type: application/json' \
     --data-binary '{"query":"mutation ScheduleNewReminder($input: ScheduleReminderInput!) {\n  scheduleReminder(input: $input) {\n    id\n    patientName\n    phoneNumber\n    appointmentTime\n    reminderTime\n    status\n    sinchBatchId\n  }\n}","variables":{"input":{"patientName":"Bob The Builder","doctorName":"Wendy","phoneNumber":"+15559876543","appointmentDate":"2025-09-10","appointmentTime":"10:00","timeZone":"Europe/London"}}}' \
     --compressed

   • Replace placeholders with valid data. Ensure the appointmentDate and appointmentTime result in a reminderTime (2 hours prior) that is in the future from when you run the test.
   • Check the response in the GraphQL playground or terminal. You should see the details of the created Reminder record.
   • Check the API server logs (yarn rw dev output) for logs from the service function.
   • Check your Sinch Dashboard (Logs or specific API logs) to see if the message scheduling request was received.

How Do You Create the React Frontend for Scheduling Reminders?

Create a React page with a form to schedule reminders.

1. Generate Page: Create a new page component for the reminder form.

   bashCopy

   yarn rw g page ReminderScheduler /schedule

   This creates web/src/pages/ReminderSchedulerPage/ReminderSchedulerPage.tsx.

2. Build the Form: Open web/src/pages/ReminderSchedulerPage/ReminderSchedulerPage.tsx and implement the form using Redwood Form components.

   typescriptCopy

   // web/src/pages/ReminderSchedulerPage/ReminderSchedulerPage.tsx
   import { MetaTags, useMutation } from '@redwoodjs/web'
   import { toast, Toaster } from '@redwoodjs/web/toast'
   import {
     Form,
     Label,
     TextField,
     DateField,
     TimeField,
     SelectField,
     Submit,
     FieldError,
     FormError,
     useForm // Import useForm for reset
   } from '@redwoodjs/forms'
   import { useEffect, useState } from 'react'
   
   // GraphQL Mutation Definition (should match api/src/graphql/reminders.sdl.ts)
   const SCHEDULE_REMINDER_MUTATION = gql`
     mutation ScheduleReminder($input: ScheduleReminderInput!) {
       scheduleReminder(input: $input) {
         id # Request necessary fields back
       }
     }
   `
   
   // Basic list of IANA time zones (add more as needed or use a library)
   const timeZones = [
     'America/New_York', 'America/Chicago', 'America/Denver', 'America/Los_Angeles',
     'America/Anchorage', 'America/Honolulu', 'Europe/London', 'Europe/Paris',
     'Asia/Tokyo', 'Australia/Sydney', 'UTC'
     // Add more relevant time zones here
   ];
   
   
   const ReminderSchedulerPage = () => {
     const formMethods = useForm() // Get form methods for reset
   
     const [createReminder, { loading, error }] = useMutation(
       SCHEDULE_REMINDER_MUTATION,
       {
         onCompleted: () => {
           toast.success('Reminder scheduled successfully!')
           formMethods.reset() // Reset form after successful submission
         },
         onError: (error) => {
           toast.error(`Error scheduling reminder: ${error.message}`)
           console.error(error)
         },
       }
     )
   
     // Get user's local timezone guess (optional, provide a default)
     const [defaultTimeZone, setDefaultTimeZone] = useState('UTC');
     useEffect(() => {
       try {
         setDefaultTimeZone(Intl.DateTimeFormat().resolvedOptions().timeZone);
       } catch (e) {
         console.warn("Could not detect browser timezone.")
       }
     }, [])
   
   
     const onSubmit = (data) => {
       console.log('Submitting data:', data)
       // The service expects separate date/time strings, so direct submission is okay
       createReminder({ variables: { input: data } })
     }
   
     return (
       <>
         <MetaTags title="Schedule Reminder" description="Schedule an SMS reminder" />
         <Toaster toastOptions={{ className: 'rw-toast', duration: 6000 }} />
   
         <h1>Schedule New Reminder</h1>
   
         <Form
           onSubmit={onSubmit}
           error={error}
           className="rw-form-wrapper"
           formMethods={formMethods}
         >
            {/* Display top-level form errors (like network issues) */}
           <FormError error={error} wrapperClassName="rw-form-error-wrapper" titleClassName="rw-form-error-title" listClassName="rw-form-error-list" />
   
           <Label name="patientName" errorClassName="rw-label rw-label-error">Patient Name</Label>
           <TextField
             name="patientName"
             validation={{ required: true }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             aria-required="true"
             aria-label="Patient Name"
           />
           <FieldError name="patientName" className="rw-field-error" />
   
           <Label name="doctorName" errorClassName="rw-label rw-label-error">Doctor Name</Label>
           <TextField
             name="doctorName"
             validation={{ required: true }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             aria-required="true"
             aria-label="Doctor Name"
           />
           <FieldError name="doctorName" className="rw-field-error" />
   
           <Label name="phoneNumber" errorClassName="rw-label rw-label-error">Phone Number (E.164 Format: +1xxxxxxxxxx)</Label>
           <TextField
             name="phoneNumber"
             placeholder="+15551234567"
             validation={{
               required: true,
               pattern: {
                 value: /^\+[1-9]\d{1,14}$/, // Basic E.164 regex
                 message: 'Please enter in E.164 format (e.g., +15551234567)',
               },
             }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             aria-required="true"
             aria-label="Phone Number"
             aria-describedby="phone-help"
           />
           <span id="phone-help" className="rw-help-text">Include country code (e.g., +1 for US)</span>
           <FieldError name="phoneNumber" className="rw-field-error" />
   
   
           <Label name="appointmentDate" errorClassName="rw-label rw-label-error">Appointment Date</Label>
           <DateField
             name="appointmentDate"
             validation={{ required: true }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             aria-required="true"
             aria-label="Appointment Date"
           />
           <FieldError name="appointmentDate" className="rw-field-error" />
   
           <Label name="appointmentTime" errorClassName="rw-label rw-label-error">Appointment Time (24-hour)</Label>
           <TimeField
             name="appointmentTime"
             validation={{ required: true }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             aria-required="true"
             aria-label="Appointment Time"
           />
           <FieldError name="appointmentTime" className="rw-field-error" />
   
           <Label name="timeZone" errorClassName="rw-label rw-label-error">Appointment Time Zone</Label>
           <SelectField
             name="timeZone"
             validation={{ required: true }}
             errorClassName="rw-input rw-input-error"
             className="rw-input"
             defaultValue={defaultTimeZone} // Set default based on browser guess
             aria-required="true"
             aria-label="Time Zone"
           >
             {timeZones.map(tz => (
               <option key={tz} value={tz}>{tz}</option>
             ))}
           </SelectField>
           <FieldError name="timeZone" className="rw-field-error" />
   
           <div className="rw-button-group">
              <Submit
                disabled={loading}
                className="rw-button rw-button-blue"
                aria-label={loading ? "Scheduling reminder..." : "Schedule Reminder"}
              >
                {loading ? (
                  <>
                    <span className="spinner" aria-hidden="true"></span>
                    Scheduling...
                  </>
                ) : (
                  'Schedule Reminder'
                )}
              </Submit>
           </div>
         </Form>
       </>
     )
   }
   
   export default ReminderSchedulerPage

   • Uses Redwood's useMutation hook to call the scheduleReminder GraphQL mutation.
   • Uses Redwood Form components (<Form>, <TextField>, <DateField>, <TimeField>, <SelectField>, <Submit>, <FieldError>, <FormError>) for structure, validation, and error handling.
   • Includes basic client-side validation (required, pattern). More complex validation happens in the service.
   • Uses Toaster for displaying success/error messages.
   • Includes a <SelectField> for selecting the appointment's time zone, crucial for correct calculation. It attempts to default to the user's browser time zone.
   • Form resets after successful submission using formMethods.reset()
   • Loading state indicator shows "Scheduling..." with spinner during submission
   • ARIA attributes for screen reader accessibility

3. Add Route: Ensure the route is defined in web/src/Routes.tsx:

   typescriptCopy

   // web/src/Routes.tsx
   import { Router, Route, Set } from '@redwoodjs/router'
   import GeneralLayout from 'src/layouts/GeneralLayout/GeneralLayout' // Example layout
   
   const Routes = () => {
     return (
       <Router>
         <Set wrap={GeneralLayout}> // Use your desired layout
            <Route path="/schedule" page={ReminderSchedulerPage} name="scheduleReminder" />
            {/* Add other routes here */}
            <Route notfound page={NotFoundPage} />
         </Set>
       </Router>
     )
   }
   
   export default Routes

4. Run and Test: Start the development server:

   bashCopy

   yarn rw dev

   Navigate to http://localhost:8910/schedule (or your configured port). Fill out the form with valid data (ensure the appointment is far enough in the future) and submit. Check the browser console, API server logs, and Sinch dashboard for confirmation. You should receive the SMS 2 hours before the specified appointment time.

How Do You Handle Errors and Implement Retry Logic?

Error Handling:

• Frontend: Uses Redwood Forms FieldError and FormError, useMutation's onError callback, and toast notifications.
• Backend (Service): Uses try...catch blocks around critical operations (validation, date/time parsing, API calls, database writes). Includes specific error messages and logs errors using Redwood's logger. Highlights the critical failure case where the SMS is scheduled but the database write fails, suggesting robust compensation logic for production.

Logging:

• Uses Redwood's built-in logger on the API side (src/lib/logger.ts). Logs key events like receiving requests, preparing data, successful API calls, database writes, and errors. Avoid logging sensitive data like SINCH_KEY_SECRET.

Implementing Retry Logic with async-retry:

Install the library:

yarn workspace api add async-retry
yarn workspace api add -D @types/async-retry

Update the service to include retry logic:

// api/src/services/reminders/reminders.ts
import retry from 'async-retry'

// Inside scheduleReminder function, replace the Sinch API call section:

// 4. Schedule SMS with Sinch API (with retry logic)
let sinchResponse;
try {
  sinchResponse = await retry(
    async (bail) => {
      try {
        return await sinchClient.sms.batches.send({
          sendSMSRequestBody: {
            to: [normalizedPhone],
            from: process.env.SINCH_FROM_NUMBER,
            body: messageBody,
            send_at: sendAtIso,
          },
        })
      } catch (error) {
        // Don't retry 4xx client errors (bad request, auth failures)
        if (error.response?.status >= 400 && error.response?.status < 500) {
          logger.error({ error, status: error.response.status }, 'Client error - not retrying')
          bail(new Error(`Client error: ${error.response?.data?.error?.message || error.message}`))
          return
        }
        // Retry 5xx server errors and network failures
        logger.warn({ error, attempt: error.attemptNumber }, 'Sinch API call failed, retrying...')
        throw error
      }
    },
    {
      retries: 3, // Maximum 3 retry attempts
      factor: 2, // Exponential backoff factor
      minTimeout: 1000, // Start with 1 second delay
      maxTimeout: 5000, // Max 5 seconds between retries
      onRetry: (error, attempt) => {
        logger.info({ attempt, maxRetries: 3 }, 'Retrying Sinch API call')
      },
    }
  )
  logger.info({ sinchResponse }, 'Successfully scheduled SMS via Sinch')
} catch (error) {
  logger.error({ error }, 'Failed to schedule SMS after all retries')
  throw new Error(`Failed to schedule SMS: ${error.message}`)
}

Error Code Handling with Recovery Strategies:

Monitoring and Alerting for Production:

1. Implement health checks:

// api/src/functions/health.ts
export const handler = async () => {
  try {
    await db.$queryRaw`SELECT 1`
    return { statusCode: 200, body: JSON.stringify({ status: 'healthy' }) }
  } catch (error) {
    return { statusCode: 503, body: JSON.stringify({ status: 'unhealthy', error: error.message }) }
  }
}

2. Track metrics: Monitor reminder scheduling success rate, average latency, and error rates

3. Set up alerts: Configure notifications for:

   • Failed reminders exceeding 5% of total
   • Database connection failures
   • Sinch API authentication errors
   • Reminders stuck in PENDING status for >24 hours

4. Implement dead letter queue: Store failed reminders in a separate table for manual review and retry

Frequently Asked Questions

What is the maximum scheduling window for Sinch SMS messages?

Sinch SMS API allows scheduling messages up to 3 days in the future using the send_at parameter. The expire_at parameter defaults to 3 days after send_at, which is also the maximum allowed value. If you need to schedule messages further in advance, implement your own queueing system or use a job scheduler like Redwood's job system to trigger the Sinch API call closer to the desired send time.

Implementing longer-term scheduling:

// api/src/services/reminders/reminders.ts
export const scheduleReminder: MutationResolvers['scheduleReminder'] = async ({ input }) => {
  // Calculate reminder time
  const reminderDateTime = appointmentDateTime.minus({ hours: 2 })
  const now = DateTime.now()
  const threeDaysFromNow = now.plus({ days: 3 })

  if (reminderDateTime > threeDaysFromNow) {
    // Store in DB without calling Sinch API yet
    const reminder = await db.reminder.create({
      data: {
        ...input,
        status: 'QUEUED', // New status for future scheduling
        reminderTime: reminderDateTime.toJSDate(),
      },
    })

    logger.info({ reminderId: reminder.id }, 'Reminder queued for future scheduling')
    return reminder
  } else {
    // Schedule immediately via Sinch API
    // ... existing scheduling logic
  }
}

// Create a cron job to process queued reminders
// api/src/functions/scheduleQueuedReminders.ts
export const handler = async () => {
  const threeDaysFromNow = DateTime.now().plus({ days: 3 })

  const queuedReminders = await db.reminder.findMany({
    where: {
      status: 'QUEUED',
      reminderTime: {
        lte: threeDaysFromNow.toJSDate(),
      },
    },
  })

  for (const reminder of queuedReminders) {
    // Schedule via Sinch API and update status to PENDING
    // ... scheduling logic
  }
}

How do you format the send_at timestamp for Sinch API?

Use ISO-8601 format with timezone information: YYYY-MM-DDThh:mm:ss.SSSZ. For example, 2025-08-22T14:30:00.000Z represents August 22, 2025 at 2:30 PM UTC. Luxon's toISO() method automatically formats DateTime objects in this format. Always convert your local appointment times to UTC before passing to the Sinch API to ensure accurate scheduling across time zones.

Which Sinch regional endpoints are available for SMS?

Sinch provides five regional SMS API endpoints:

Region selection criteria:

1. Data residency requirements: EU companies often must use EU region for GDPR compliance
2. User base location: Choose closest region to majority of recipients
3. Latency requirements: Critical for time-sensitive reminders
4. Account provisioning: Check which regions your Sinch account supports

How do you handle time zones correctly in RedwoodJS SMS scheduling?

Use Luxon's DateTime object with explicit time zone information. Accept the user's time zone as input (using IANA time zone names like America/New_York), parse the appointment date/time in that zone using DateTime.fromISO(dateTimeString, { zone: timeZone }), then convert to UTC with .toUTC() before storing in the database and sending to Sinch. This ensures reminders send at the correct local time regardless of server location.

What database fields do you need for SMS reminder tracking?

Store these essential fields in your Prisma schema:

Index status and reminderTime together for efficient queries when building admin dashboards or cleanup jobs:

@@index([status, reminderTime])

How do you validate phone numbers for Sinch SMS in RedwoodJS?

Use E.164 format validation (/^\+[1-9]\d{1,14}$/ regex) for basic checking, but implement the libphonenumber-js library for production applications.

Installing and using libphonenumber-js:

yarn workspace api add libphonenumber-js

// api/src/services/reminders/reminders.ts
import { parsePhoneNumber, isValidPhoneNumber } from 'libphonenumber-js'

const normalizePhoneNumber = (inputPhone: string, defaultCountry = 'US'): string => {
  try {
    // Validate format
    if (!isValidPhoneNumber(inputPhone, defaultCountry)) {
      throw new Error(`Invalid phone number: ${inputPhone}`)
    }

    // Parse and format to E.164
    const phoneNumber = parsePhoneNumber(inputPhone, defaultCountry)
    return phoneNumber.format('E.164') // Returns +12025550187
  } catch (error) {
    logger.error({ error, inputPhone }, 'Phone validation failed')
    throw new Error('Enter a valid phone number with country code (e.g., +1 555 123 4567)')
  }
}

Supported input formats (all convert to +12025550187):

• +1 202 555 0187 (international with spaces)
• (202) 555-0187 (US local format)
• 202-555-0187 (US dashed format)
• 2025550187 (digits only, with country hint)

What happens if the SMS scheduling fails but the database save succeeds?

This is a critical consistency issue. The example code includes a try...catch around the database save after successful Sinch scheduling. If the database write fails, the SMS is already scheduled but you have no record. Production systems need compensation logic: save the reminder with status PENDING before calling Sinch, then update to SCHEDULED after success. Alternatively, log the sinchBatchId to a failure tracking system and implement a reconciliation job that queries Sinch API to identify orphaned scheduled messages.

How do you implement retry logic for failed Sinch API calls in RedwoodJS?

Use the async-retry npm package in your service function. Wrap the sinchClient.sms.batches.send() call with retry logic that handles transient network errors (connection timeouts, 5xx responses) but not permanent failures (4xx authentication or validation errors). Implement exponential backoff (e.g., 1s, 2s, 4s delays) with a maximum of 3-5 retry attempts. Log each retry attempt using RedwoodJS logger and update the reminder status to FAILED if all retries exhaust.

See the complete implementation in the "How Do You Handle Errors and Implement Retry Logic?" section above.