Use Next.js API routes to securely handle server-side communication with the Sinch SMS REST API. Create a form on your frontend to collect recipient and message details. The API route fetches data from the form and sends it to Sinch, keeping your API keys hidden from the client-side.

The Sinch SMS REST API is a service that allows you to send SMS messages programmatically. This guide uses the `/batches` endpoint for sending outbound messages from a Next.js application.

Zod provides robust input validation, ensuring data integrity and preventing invalid requests from reaching the Sinch API, thus enhancing security and preventing errors. This guide uses it to validate phone numbers (E.164 format) and message content within the API route.

Always use environment variables for sensitive data like API keys and secrets to protect them from being exposed in your code repository or the browser. This guide stores Sinch credentials in `.env.local`, which is only accessible server-side.

Yes, but ensure your Sinch account and numbers are enabled for international sending. Use the E.164 phone number format (+countrycodeNUMBER) enforced by the provided Zod schema. International costs may vary, so check Sinch's pricing.

Create a `.env.local` file in your project root and add `SINCH_SERVICE_PLAN_ID`, `SINCH_API_TOKEN`, `SINCH_NUMBER` (your Sinch phone number), and `SINCH_REGION_URL`. Get these values from your Sinch Dashboard under SMS > APIs, and ensure your number is linked to your service plan ID.

The `/batches` endpoint is the standard Sinch REST API endpoint for sending one or more SMS messages. It's the most versatile and commonly used way to trigger messages programmatically, as demonstrated in this guide.

Next.js has built-in CSRF protection mechanisms that enhance security for form submissions and other interactions. Since this example uses API route calls initiated from the same origin, it generally benefits from these default protections, reducing vulnerabilities.

Double-check your `SINCH_API_TOKEN` and `SINCH_SERVICE_PLAN_ID` in your `.env.local` file against your Sinch Dashboard. Ensure they are correct and haven't been revoked. Also, verify you're using Bearer Token authentication (`Authorization: Bearer YOUR_TOKEN`) and restart the development server.

The Sinch API handles long messages (exceeding standard SMS length limits) by splitting them into multiple parts (concatenated SMS). The provided code allows up to 1600 characters, reflecting this. Be aware of potential extra costs per segment, particularly with international sending.

Validating input, especially phone numbers, ensures the message is sent to the intended recipient and prevents unexpected errors or abuse of the Sinch API. The Zod library, demonstrated in this guide, prevents bad data from reaching the API and provides clear error messages.

Check your server-side logs for detailed error messages from both your API route and the Sinch API response. Verify environment variables, phone number formatting (E.164), and ensure the correct `SINCH_REGION_URL` is used. Refer to the troubleshooting section for common error codes and solutions.

Implement structured logging (JSON format) in your API route using a library like Pino or Winston. Send these logs to a centralized logging service like Datadog, Logtail, or Axiom for analysis and alerting, particularly in a production environment.

For high throughput, use a message queue (like BullMQ) to handle asynchronous sending. Offload the Sinch API call to a background worker, allowing the API route to respond quickly without blocking. Monitor Sinch's rate limits and API concurrency to optimize performance.

Platforms like Vercel are well-suited. Push your project to a Git repository (excluding `.env.local`), connect it to Vercel, and set your environment variables in the Vercel dashboard to securely manage your Sinch API credentials.