Use a reputable SMS API provider like Twilio, Sinch, MessageBird, or Plivo. Ensure the recipient numbers are in E.164 format (+385XXXXXXXXX) and comply with Croatian regulations. Remember that two-way SMS is not supported.

Standard SMS length limits apply: 160 characters for GSM-7 encoding and 70 characters for UCS-2. Concatenated messages are supported for longer texts, but special characters reduce the limit per segment as they require UCS-2 encoding.

MMS messages are automatically converted to SMS with an embedded URL link in Croatia to guarantee compatibility across devices while still allowing sharing of rich media content through web pages.

The best practice is between 8:00 AM and 8:00 PM local time, avoiding Sundays and national holidays. Adhere to consent and opt-out regulations while respecting recipient preferences.

No, sending SMS to landline numbers in Croatia is not supported. Attempts to do so will result in failed delivery and a specific error response (400 error code 21614) from the SMS API without incurring charges.

Explicit consent is required for marketing messages. This must be freely given, specific, and informed, either in written or electronic form. Maintain clear records of consent, including the date, time, and method of collection.

All marketing messages must include clear opt-out instructions. The STOP command must be honored in both Croatian ("STOP") and English, with an immediate confirmed response. Other keywords like "POMO??" (HELP) should also be supported.

Alphanumeric sender IDs are supported, and dynamic usage is allowed without pre-registration. However, be aware that the sender ID is not guaranteed to be preserved and may be overwritten by the A1 network.

Long codes are supported for both domestic and international messaging with good delivery rates and sender ID preservation for international codes. They're ideal for transactional messages, 2FA, and customer support, with provisioning typically taking 1-2 business days.

Implement queue systems, use batch APIs, incorporate exponential backoff for retries, and monitor throughput and adjust as needed to manage high-volume SMS campaigns effectively.

The Croatian Regulatory Authority for Network Industries (HAKOM) oversees telecommunications, enforcing regulations related to SMS communication, including compliance with the Electronic Communications Act.

Restricted content includes gambling (requires special permits), adult content (prohibited), cryptocurrency (subject to financial regulations), and political messaging (special requirements during elections). Avoid spam trigger words and ensure URLs are from trusted domains.

Default to Croatian, offer language preferences, use proper diacritical marks, and consider regional dialects for targeted campaigns. Ensure all communications respect local customs and language nuances.

Process opt-outs within 24 hours, maintain a centralized opt-out database, confirm the opt-out via SMS, and regularly audit for compliance. Respecting user preferences is crucial for maintaining good practice.

Twilio: 100/second, Sinch: 30/second, MessageBird: 60/second, and Plivo: 50/second. Remember to implement strategies like queuing and backoff for high-volume sending to stay within these limits.