Frequently Asked Questions
Use the Sinch SMS REST API with a Node.js Express app. This allows you to send a single message to multiple recipients by making a POST request to the /batches endpoint. The request should include an array of phone numbers and the message content. This approach is significantly more efficient than sending individual messages and allows for scalable broadcasts.
The Sinch /batches endpoint is designed for efficient bulk SMS messaging. It enables sending the same SMS message to multiple recipients in a single API call, rather than sending numerous individual messages, thus optimizing performance and cost-effectiveness. It expects an array of recipient phone numbers and the message body in the request payload.
Store your Sinch `SERVICE_PLAN_ID`, `API_TOKEN`, `SINCH_NUMBER`, and `SINCH_BASE_URL` as environment variables in a `.env` file. Use the `dotenv` package in your Node.js project to load these variables into your application's environment. This practice keeps your credentials out of your codebase, enhancing security.
Bulk SMS sending leverages Sinch's optimized infrastructure to deliver messages to multiple recipients with a single API call. This reduces overhead compared to iteratively sending individual messages, resulting in improved speed and efficiency. The Sinch /batches endpoint is specifically designed for this type of broadcast.
Consider a message queue for high-volume bulk SMS sending, typically for broadcasts reaching tens of thousands of recipients or more. Queuing decouples the API request from the actual SMS delivery process, enabling your application to handle requests quickly without being slowed down by the time it takes to submit the batch to the Sinch API.
Always use the E.164 format for recipient phone numbers when sending SMS messages via the Sinch API. This international standard includes a plus sign (+), the country code, and the subscriber number without any spaces or dashes (e.g., +12025550147). Proper formatting is crucial for successful delivery.
Yes, you can enable delivery reports (DLRs) in your Sinch API requests and configure a webhook URL in your Sinch account settings. Sinch will then send POST requests to your specified webhook URL with delivery updates for each message. This allows you to track successful deliveries, failures, and other delivery statuses.
Implement robust error handling by catching potential errors from Axios when making requests to the Sinch API. Inspect the error object, specifically `error.response.data` for detailed information provided by Sinch about the issue. Handle different error codes (4xx, 5xx) appropriately, providing informative error messages and potentially retrying requests for transient errors.
Log key information such as incoming request details, successful batch submissions with batch IDs, and any errors encountered. For errors, include detailed information from the Sinch API response, such as status codes and error messages. Use a structured logging format, like JSON, for easier parsing and analysis in production environments.
Use the `express` package in Node.js to create an app, define routes, and handle requests. Set up middleware to parse JSON request bodies (`app.use(express.json())`). Define an API endpoint, such as `/api/broadcast`, to handle the incoming requests for sending bulk SMS messages. Include error handling middleware to catch and process errors gracefully.
Axios is a promise-based HTTP client used to make HTTP requests to the Sinch API from your Node.js application. It simplifies the process of making API calls, handling responses, and managing asynchronous operations. Axios also provides features for handling errors and network issues.
Protect your API keys by storing them in environment variables (`.env`) and excluding this file from version control (`.gitignore`). Implement input validation and sanitization to prevent invalid data from reaching the Sinch API. Consider using rate limiting to protect against abuse. Run your app behind HTTPS and implement authentication/authorization if needed.
Common errors include 401 Unauthorized (check API credentials), 400 Bad Request (verify phone numbers, request body), 403 Forbidden (check number permissions), and 5xx Server Errors (retry with backoff). Carefully inspect `error.response.data` for detailed error messages from Sinch to diagnose and resolve issues.
Create a clear project structure with directories like `src/`, `controllers/`, `routes/`, `services/`. This promotes maintainability. The `src/app.js` file initializes the Express app, `controllers` handle request logic, `routes` define endpoints, and `services` encapsulate API interaction logic.
Build a Node.js Express App for Bulk SMS Broadcasts with Sinch
This guide provides a step-by-step walkthrough for building a robust Node.js application using the Express framework to send bulk SMS messages via the Sinch REST API. We'll cover everything from project setup and core logic to error handling, security, and deployment considerations.
By the end of this tutorial, you will have a functional backend service capable of accepting a list of phone numbers and a message, then broadcasting that message efficiently using Sinch's batch sending capabilities. This solves the common need for applications to send notifications, alerts, or marketing messages to multiple users simultaneously.
Project Overview and Goals
What We're Building:
A Node.js Express API endpoint that:
/batches
endpoint) to send the message to all recipients in a single API call (a bulk broadcast).Problem Solved:
Manually sending SMS messages one by one is inefficient and doesn't scale. This application provides a programmatic way to broadcast messages to large groups, leveraging Sinch's infrastructure for reliable delivery.
Technologies Used:
/batches
endpoint for efficient bulk sending..env
file, keeping sensitive credentials out of the codebase.System Architecture:
The basic flow is as follows:
/api/broadcast
on the Node.js Express App./v1/batches
endpoint.Prerequisites:
SERVICE_PLAN_ID
: Found on your Sinch Customer Dashboard under SMS > APIs.API_TOKEN
: Also found on the same page (click ""Show"" to reveal it).SINCH_NUMBER
: A virtual number associated with your Service Plan ID, capable of sending SMS. Find this by clicking your Service Plan ID link on the dashboard.curl
for testing the API endpoint.Expected Outcome:
A running Node.js service with an API endpoint (
/api/broadcast
) that accepts recipient lists and messages, sending them out via Sinch.1. Setting up the Project
Let's initialize our Node.js project, install dependencies, and set up the basic structure and environment configuration.
Create Project Directory: Open your terminal or command prompt and create a new directory for the project.
Initialize Node.js Project: This creates a
package.json
file to manage project details and dependencies.(The
-y
flag accepts default settings)Install Dependencies: We need Express for the web server, Axios for API calls, and dotenv for environment variables.
Create Project Structure: A good structure helps maintainability. Create the following directories and files:
Create
.gitignore
: Prevent sensitive files and unnecessary directories from being committed to version control. Create a file named.gitignore
in the root directory:Configure Environment Variables: Create a file named
.env
in the root directory. This file will hold your sensitive Sinch credentials and configuration. Never commit this file to Git.Service plan ID
andAPI token
. Also, find a virtualSinch Number
associated with this plan.us.sms.api.sinch.com
,eu.sms.api.sinch.com
).Populate the
.env
file:SINCH_SERVICE_PLAN_ID
: Your unique service plan identifier from the Sinch dashboard.SINCH_API_TOKEN
: The secret token used to authenticate API requests. Treat this like a password.SINCH_NUMBER
: The Sinch virtual phone number that messages will be sent from. Must be in E.164 format (e.g.,+1xxxxxxxxxx
).SINCH_BASE_URL
: The base URL for the Sinch REST API corresponding to your account's region. Ensure this matches your dashboard.PORT
: The port your Express application will listen on.Set up Basic Express Server (
src/app.js
): This file initializes Express, loads environment variables, sets up middleware, and defines the entry point for our routes.""type"": ""module""
to yourpackage.json
file to enable ES module syntax (import
/export
).2. Implementing Core Functionality (Sinch Service)
Now, let's create the service responsible for interacting with the Sinch API.
Create Sinch Service (
src/services/sinchService.js
): This module encapsulates the logic for sending the bulk SMS batch request./batches
Endpoint: This specific Sinch API endpoint is designed for sending the same message to multiple recipients efficiently.from
,to
(an array), andbody
fields. Refer to the Sinch API Documentation for more optional parameters likedelivery_report
.Bearer
token scheme in theAuthorization
header.3. Building the API Layer (Routes & Controller)
Let's define the API endpoint that clients will call to trigger the broadcast.
Create Broadcast Controller (
src/controllers/broadcastController.js
): This handles incoming requests for the broadcast endpoint, validates input, calls thesinchService
, and sends the response.recipients
andmessage
. Includes a basic E.164 format check as an example of stricter validation. Consider using a dedicated validation library likeexpress-validator
orjoi
for production apps.sendBulkSms
function from our service.202 Accepted
status on success, indicating the batch was submitted but processing (delivery) is asynchronous. Includes thebatch_id
from Sinch, which is crucial for tracking.next(error)
to pass any caught errors to the centralized error handler defined inapp.js
.Create Broadcast Routes (
src/routes/broadcastRoutes.js
): This file defines the specific API endpoint and maps it to the controller function.express.Router()
to create a modular set of routes.POST
method on the/broadcast
path (which becomes/api/broadcast
due to the prefix inapp.js
) to thehandleBroadcastRequest
controller function.4. Integrating with Sinch (Recap)
Integration primarily happens within
src/services/sinchService.js
:SINCH_SERVICE_PLAN_ID
,SINCH_API_TOKEN
,SINCH_NUMBER
, andSINCH_BASE_URL
from environment variables (.env
) usingdotenv
.axios
to make aPOST
request to the Sinch/batches
endpoint (${BASE_URL}/xms/v1/${SERVICE_PLAN_ID}/batches
).Authorization: Bearer ${API_TOKEN}
header.from
,to
(array), andbody
..env
and using.gitignore
prevents accidental exposure. Ensure your deployment environment securely manages these variables.5. Error Handling, Logging, and Retry Mechanisms
handleBroadcastRequest
) with specific 400 Bad Request responses.sinchService
, enriched with details and status code if possible, then re-thrown. These are caught again in the controller and passed vianext(error)
to the global error handler inapp.js
, which sends a generic 500 Internal Server Error (or the specific status from the service error).app.js
provides a consistent response format for unexpected server errors.console.log
for request tracking (app.js
), successful submissions, and errors (sinchService.js
,broadcastController.js
).console.log
with a more robust logging library like Winston or Pino. These enable:batch_id
.axios-retry
can simplify adding retry logic to Axios requests.POST
request might result in duplicate batches being sent if the initial request succeeded but the response was lost. Consider adding a uniqueclient_reference
in the payload if you implement retries, although Sinch doesn't explicitly guarantee idempotency based on it for the/batches
endpoint. It's often safer to log the failure and investigate manually or use a more sophisticated queuing system for critical broadcasts that require guaranteed exactly-once processing. For this guide, we'll rely on logging failures.6. Database Schema and Data Layer (Optional Enhancement)
While this guide focuses on accepting recipients directly via the API, a common scenario involves fetching recipients from a database.
Schema Example (Conceptual): If using a relational database (like PostgreSQL) with an ORM (like Prisma or Sequelize), you might have a
Subscriber
table:Entity Relationship Diagram Description (Simple): A more advanced implementation might track broadcasts and recipient status:
SUBSCRIBER
table (as above) stores user phone numbers.BROADCAST
table stores information about each bulk message sent (e.g., message body, Sinch batch ID, timestamp).BROADCAST_RECIPIENT
table linksSUBSCRIBER
andBROADCAST
, potentially storing the delivery status for each recipient in a specific broadcast (updated via webhooks).Data Access: You would modify the
handleBroadcastRequest
controller:req.body.recipients
, maybe accept agroupId
or similar identifier.subscribersService.getActiveSubscribers(groupId)
) to query the database for active phone numbers.sinchService.sendBulkSms
.Implementation: Setting up a database, ORM, migrations, and data access functions is beyond the scope of this guide but is a common next step. Tools like Prisma or Sequelize are excellent choices in the Node.js ecosystem.
7. Adding Security Features
Security is paramount, especially when handling user data and API keys.
DOMPurify
(if rendering) or basic escaping might be relevant depending on context. For this API, strict validation is key.express-rate-limit
.src/app.js
):.env
and.gitignore
.8. Handling Special Cases
+
followed by country code and number, no spaces or dashes) before sending to Sinch.SINCH_NUMBER
is enabled for international sending if broadcasting globally. Message content localization would need to be handled by your application logic before calling the API.delivery_report: 'full'
(or other level) in the/batches
payload.9. Implementing Performance Optimizations
/batches
endpoint is the single most significant optimization for bulk sending, reducing network latency and API call overhead compared to sending individual messages.202 Accepted
).sinchService
.phone_number
,is_active
, etc.). Fetch only the necessary data (phone_number
).axios
and standard Node.js operations do). Avoid CPU-bound tasks on the main event loop thread for high-throughput scenarios.10. Adding Monitoring, Observability, and Analytics
For production readiness, visibility into your application's health and performance is vital.
/healthz
) that returns a200 OK
status. Monitoring systems can ping this to verify the service is running./api/broadcast
endpoint.prom-client
to expose metrics in Prometheus format, then visualize them in Grafana. Cloud providers often have integrated monitoring solutions.app.js
with Sentry - conceptual):11. Troubleshooting and Caveats
error.response.data
):401 Unauthorized
: InvalidAPI_TOKEN
orSERVICE_PLAN_ID
. Double-check credentials in.env
and the Sinch dashboard.400 Bad Request
: Often due to invalid phone number format (ensure E.164), missing required fields (from
,to
,body
), or issues with theSINCH_NUMBER
(e.g., not provisioned correctly). Check the detailed error message from Sinch.403 Forbidden
: TheSINCH_NUMBER
might not be allowed to send messages to a specific region, or the account might have restrictions.5xx Server Error
: Temporary issue on Sinch's side. Consider implementing retries with backoff for these.429 Too Many Requests
errors appropriately (e.g., by slowing down requests or using backoff).202 Accepted
with abatch_id
) only means Sinch accepted the batch, not that messages were delivered. Use Delivery Reports (Webhooks) for actual delivery confirmation.