Set up a dedicated API route within your Next.js application using Node.js. This API endpoint acts as a webhook, receiving callback events from Sinch like message delivery updates or inbound messages. The setup involves installing necessary dependencies such as raw-body and configuring environment variables, including a secret key for HMAC signature validation and Sinch credentials. Project structure and environment variables are crucial for this setup process

Sinch webhooks allow your application to receive real-time updates on events like message delivery status (delivered, failed) and inbound messages. Since Sinch operates asynchronously, the initial API call only confirms message acceptance, not delivery. Webhooks solve this by providing a way for your application to be notified of these asynchronous events, enabling features like delivery receipts and real-time chat.

Sinch uses HMAC (Hash-Based Message Authentication Code) to ensure that callbacks received by your webhook are genuinely from Sinch and haven't been tampered with. HMAC involves a shared secret between your app and Sinch, which is used to generate a unique signature for each callback. By verifying this signature, you can confirm the authenticity and integrity of the callback data.

Use message delivery callbacks whenever you need to track the status of messages sent through the Sinch API. This is important for providing delivery receipts to users, updating message status in your application's UI, or triggering automated actions based on successful or failed delivery. Callbacks are essential because Sinch's message sending is asynchronous.

The Sinch webhook secret is a crucial security measure for authenticating callbacks. It's a strong, random string that you generate and share with Sinch when configuring your webhook. It's used as part of the HMAC signature calculation, ensuring only Sinch can generate valid signatures, thus protecting against unauthorized requests.

Sinch automatically retries callbacks if your endpoint doesn't respond with a 2xx status code within a timeout. Implement idempotent processing logic in your Next.js webhook handler to handle these retries. Ensure that processing the same callback multiple times doesn't lead to incorrect application behavior, for example, by checking for existing database entries before inserting new ones.

Verify the signature by comparing the calculated HMAC with the one received in the x-sinch-webhook-signature header. Use the raw request body, nonce, timestamp, and your shared secret to calculate the expected signature. Critically, get the raw body before any JSON parsing. Return a 401 Unauthorized error if the signatures don't match.

Respond to Sinch with a 200 OK status immediately upon receiving the callback. Then, offload the actual processing logic, like database updates or notifications, to a separate asynchronous function. This prevents Sinch from retrying due to slow processing times.

Use ngrok to create a secure tunnel to your locally running Next.js development server. This provides a public HTTPS URL that Sinch can send callbacks to. Remember that the ngrok URL changes on restart, requiring frequent Sinch webhook updates during development.

Yes, you can use Prisma to persist callback data. Define a Prisma schema with models to represent the information you want to store, such as message status, IDs, and timestamps. Use the Prisma client in your webhook handler to perform database operations asynchronously after acknowledging Sinch with a 200 OK response. It's crucial here also to handle retries (idempotency) properly.

Select the Sinch callback triggers according to the events you need to track. MESSAGE_DELIVERY tracks delivery status updates. MESSAGE_INBOUND tracks incoming messages to your application. EVENT_INBOUND is useful for features like typing indicators. OPT_IN and OPT_OUT handle user consent management.

Sinch retries callbacks, so your processing logic needs to be idempotent. Before performing any action, like updating a database record, verify that the callback hasn't already been processed. Check for existing entries based on message ID or event ID. Prisma's upsert functionality is useful for ensuring idempotency.

Check the webhook URL configured in the Sinch portal for accuracy, including typos and HTTP/HTTPS mismatches. Examine server logs for errors. If using ngrok, ensure it's running and the URL is active. Verify that the webhook secret matches the one in your environment variables.

HMAC validation failures typically result from mismatched secrets between your app and the Sinch configuration, issues with raw body processing (ensure you're hashing the raw body before JSON parsing), or missing or incorrect signature headers. Double-check these aspects, and log the raw body and headers for debugging.