This guide provides a step-by-step walkthrough for building a production-ready NestJS application capable of sending SMS messages using the MessageBird API and its Node.js SDK. We will cover project setup, core implementation, configuration, error handling, security, testing, and deployment considerations.

By the end of this guide, you will have a robust API endpoint that accepts a recipient phone number and a message body, validates the input, and uses MessageBird to reliably deliver the SMS. This solves the common need for programmatic SMS notifications, alerts, or basic communication features within a modern web application.

Project Overview and Goals

• Goal: Create a simple NestJS API endpoint (POST /sms/send) to send outbound SMS messages via MessageBird.

• Problem Solved: Enables applications to programmatically send SMS messages for various purposes like notifications, verification codes (though MessageBird's Verify API is often better suited for OTP), or simple alerts.

• Technologies:

  • Node.js: The underlying runtime environment.
  • NestJS: A progressive Node.js framework for building efficient, reliable, and scalable server-side applications. Chosen for its robust structure, dependency injection, modularity, and built-in support for features like validation and configuration management.
  • MessageBird Node.js SDK: Simplifies interaction with the MessageBird REST API.
  • dotenv / @nestjs/config: For managing environment variables securely.
  • class-validator / class-transformer: For robust request payload validation.
  • libphonenumber-js (Optional): For stricter phone number validation.

• Architecture:

  Client (e.g., Postman, Frontend App)
      |
      | HTTP POST Request (/sms/send)
      V
  NestJS Application
      |  - Controller (Handles request, validation using DTO)
      |  - Service (Contains business logic, interacts with MessageBird SDK)
      |  - Module (Organizes components)
      |  - ConfigModule (Loads environment variables)
      V
  MessageBird SDK
      |
      | API Call (messages.create)
      V
  MessageBird API
      |
      | SMS Delivery Network
      V
  Recipient's Phone
  

• Prerequisites:

  • Node.js (LTS version recommended) and npm/yarn installed.
  • A MessageBird account (Free trial available).
  • A text editor or IDE (e.g., VS Code).
  • Basic understanding of TypeScript, Node.js, and REST APIs.
  • A purchased virtual number or registered Alphanumeric Sender ID in your MessageBird account to use as the originator.

1. Setting up the Project

Let's initialize our NestJS project and install the necessary dependencies.

1. Install NestJS CLI: If you don't have it, install the NestJS command-line interface globally.

   bash

   npm install -g @nestjs/cli
   

2. Create New NestJS Project: Generate a new project using the CLI.

   bash

   nest new nestjs-messagebird-sms
   

   Choose your preferred package manager (npm or yarn) when prompted.

3. Navigate to Project Directory:

   bash

   cd nestjs-messagebird-sms
   

4. Install Dependencies: We need the MessageBird SDK, and packages for configuration management and validation.

   bash

   # Using npm
   npm install messagebird @nestjs/config dotenv class-validator class-transformer
   
   # Using yarn
   yarn add messagebird @nestjs/config dotenv class-validator class-transformer
   
   • messagebird: The official Node.js SDK for the MessageBird API.
   • @nestjs/config: Handles environment variables gracefully within NestJS.
   • dotenv: Loads environment variables from a .env file into process.env. Used by @nestjs/config.
   • class-validator & class-transformer: Enable easy implementation of validation rules using decorators on DTOs (Data Transfer Objects).

5. Project Structure: The Nest CLI sets up a standard structure (src/ contains app.module.ts, app.controller.ts, app.service.ts, main.ts). We will create dedicated modules, services, and controllers for SMS functionality.

2. Configuring Environment Variables

Sensitive information like API keys should never be hardcoded. We'll use environment variables.

1. Get MessageBird API Key:

   • Log in to your MessageBird Dashboard.
   • Navigate to the Developers section in the left-hand menu.
   • Click on API access.
   • You can use your live API key or switch to test mode to get a test key. For initial development, the test key is sufficient and won't incur charges or send actual SMS. Copy the appropriate key.
   • Important: Keep your live API key secure and confidential.

2. Get MessageBird Originator:

   • This is the sender ID displayed on the recipient's phone. It can be:
     • A virtual mobile number purchased from MessageBird (e.g., +12025550134). Ensure it's SMS-enabled.
     • An Alphanumeric Sender ID (e.g., MyCompany) registered and approved in your MessageBird account (availability and regulations vary by country).
   • Find or purchase/register this in the ""Numbers"" section of the MessageBird Dashboard.

3. Create .env File: In the root directory of your project, create a file named .env.

   bash

   touch .env
   

4. Add Variables to .env: Add your MessageBird API key and originator to the file. Replace placeholders with your actual values.

   bash

   # .env
   
   # MessageBird Configuration
   MESSAGEBIRD_API_KEY=YOUR_API_KEY # Use 'test_...' or 'live_...' key
   MESSAGEBIRD_ORIGINATOR=YOUR_SENDER_ID # e.g., +12025550134 or MyCompany
   

5. Ignore .env File: Add .env to your .gitignore file to prevent accidentally committing secrets.

   # .gitignore
   # ... other entries
   .env
   

6. Configure NestJS ConfigModule: Import and configure ConfigModule in your main application module (src/app.module.ts) to make environment variables accessible throughout the application via dependency injection.

   typescript

   // src/app.module.ts
   import { Module } from '@nestjs/common';
   import { ConfigModule } from '@nestjs/config'; // Import ConfigModule
   import { AppController } from './app.controller';
   import { AppService } from './app.service';
   import { SmsModule } from './sms/sms.module'; // We will create this next
   
   @Module({
     imports: [
       ConfigModule.forRoot({ // Configure ConfigModule
         isGlobal: true, // Make ConfigService available globally
         envFilePath: '.env', // Specify the env file path
       }),
       SmsModule, // Import our SMS module
     ],
     controllers: [AppController],
     providers: [AppService],
   })
   export class AppModule {}
   
   • isGlobal: true makes the ConfigService available in any module without needing to import ConfigModule everywhere.
   • envFilePath: '.env' tells the module where to find the environment file.

3. Implementing Core SMS Functionality (Service)

We'll create a dedicated module and service to handle SMS logic.

1. Generate SMS Module and Service: Use the Nest CLI.

   bash

   nest generate module sms
   nest generate service sms
   

   This creates src/sms/sms.module.ts and src/sms/sms.service.ts (along with a test file).

2. Implement SmsService: Open src/sms/sms.service.ts and add the logic to interact with the MessageBird SDK.

   typescript

   // src/sms/sms.service.ts
   import { Injectable, Logger } from '@nestjs/common';
   import { ConfigService } from '@nestjs/config';
   import * as MessageBird from 'messagebird'; // Import MessageBird SDK types if available, or use as namespace
   
   @Injectable()
   export class SmsService {
     private readonly logger = new Logger(SmsService.name);
     private messagebird: MessageBird.MessageBird; // Declare messagebird client instance using SDK types
     private originator: string;
   
     constructor(private configService: ConfigService) {
       // Retrieve API key and originator from environment variables
       const apiKey = this.configService.get<string&gt;('MESSAGEBIRD_API_KEY');
       this.originator = this.configService.get<string&gt;('MESSAGEBIRD_ORIGINATOR');
   
       if (!apiKey || !this.originator) {
         this.logger.error('MessageBird API Key or Originator not configured in .env file');
         throw new Error('MessageBird environment variables missing.');
       }
   
       // Initialize the MessageBird client
       // The require('messagebird')(key) pattern is common for initializing CJS modules like this SDK.
       // Using 'any' here if specific types for the initializer function aren't readily available or inferred.
       try {
           const mbInitializer: any = require('messagebird');
           this.messagebird = mbInitializer(apiKey);
           this.logger.log('MessageBird SDK initialized successfully.');
       } catch (error) {
           this.logger.error('Failed to initialize MessageBird SDK', error);
           throw error; // Re-throw to prevent service usage if initialization fails
       }
     }
   
     /**
      * Sends an SMS message using the MessageBird API.
      * @param recipient - The recipient's phone number (E.164 format recommended).
      * @param body - The text content of the SMS message.
      * @returns Promise resolving with the MessageBird API response or rejecting with an error.
      */
     async sendSms(recipient: string, body: string): Promise<any&gt; { // Consider defining a stricter return type based on expected MessageBird response
       const params: MessageBird.MessageParameters = {
         originator: this.originator,
         recipients: [recipient], // Expects an array of recipients
         body: body,
       };
   
       this.logger.log(`Attempting to send SMS to ${recipient} from ${this.originator}`);
   
       // The MessageBird SDK's messages.create uses a callback.
       // We wrap it in a Promise for modern async/await usage.
       return new Promise((resolve, reject) =&gt; {
         this.messagebird.messages.create(params, (err, response) =&gt; {
           if (err) {
             this.logger.error(`Failed to send SMS to ${recipient}`, err);
             // Provide more context if available in the error object
             const errorDetails = err.errors ? JSON.stringify(err.errors) : err.message;
             reject(new Error(`MessageBird API Error: ${errorDetails}`));
           } else {
             this.logger.log(`SMS sent successfully to ${recipient}. Message ID: ${response.id}`);
             // The response contains details about the sent message(s)
             resolve(response);
           }
         });
       });
     }
   }
   
   • Dependencies: We inject ConfigService to access environment variables. Logger provides built-in NestJS logging.
   • Initialization: The constructor retrieves the API key and originator, then initializes the messagebird client. Robust error handling is added for missing variables or initialization failure. The comment clarifies the use of require and any for CJS interop.
   • sendSms Method:
     • Takes recipient and body as arguments.
     • Constructs the params object required by messagebird.messages.create, using the configured originator.
     • Wraps the callback-based SDK call in a Promise for compatibility with NestJS's async/await patterns.
     • Logs success or failure using the Logger.
     • Resolves with the MessageBird response on success, rejects with a formatted error on failure.

3. Update SmsModule: Ensure SmsService is listed as a provider in src/sms/sms.module.ts. Nest CLI usually does this automatically.

   typescript

   // src/sms/sms.module.ts
   import { Module } from '@nestjs/common';
   import { SmsService } from './sms.service';
   // If we add a controller later, import it here
   import { SmsController } from './sms.controller'; // Import controller
   
   @Module({
     controllers: [SmsController], // Add controller when created
     providers: [SmsService],
     exports: [SmsService], // Export service if needed by other modules
   })
   export class SmsModule {}
   

4. Building the API Layer (Controller and DTO)

Now, let's create the API endpoint to trigger the SmsService.

1. Generate SMS Controller:

   bash

   nest generate controller sms
   

   This creates src/sms/sms.controller.ts.

2. Create Request DTO: Create a Data Transfer Object (DTO) to define the expected shape and validation rules for the request body. Create a file src/sms/dto/send-sms.dto.ts.

   typescript

   // src/sms/dto/send-sms.dto.ts
   import { IsNotEmpty, IsString, MinLength, IsPhoneNumber } from 'class-validator';
   
   export class SendSmsDto {
     @IsNotEmpty({ message: 'Recipient phone number is required.' })
     // Use IsPhoneNumber for stricter E.164 validation.
     // Requires installing libphonenumber-js: run 'npm install libphonenumber-js' or 'yarn add libphonenumber-js'
     // @IsPhoneNumber(null, { message: 'Recipient must be a valid phone number (E.164 format recommended).' })
     @IsString() // Use IsString for a basic check if libphonenumber-js is not installed
     readonly recipient: string;
   
     @IsNotEmpty({ message: 'Message body cannot be empty.' })
     @IsString()
     @MinLength(1, { message: 'Message body must contain at least 1 character.' })
     readonly body: string;
   }
   
   • We use decorators from class-validator (@IsNotEmpty, @IsString, @MinLength, optionally @IsPhoneNumber) to define validation rules.
   • Clear instructions are added for installing libphonenumber-js if @IsPhoneNumber is used.

3. Implement SmsController: Open src/sms/sms.controller.ts and define the endpoint.

   typescript

   // src/sms/sms.controller.ts
   import { Controller, Post, Body, UsePipes, ValidationPipe, Logger, HttpException, HttpStatus } from '@nestjs/common';
   import { SmsService } from './sms.service';
   import { SendSmsDto } from './dto/send-sms.dto';
   
   @Controller('sms') // Route prefix for this controller
   export class SmsController {
     private readonly logger = new Logger(SmsController.name);
   
     constructor(private readonly smsService: SmsService) {}
   
     @Post('send') // Route: POST /sms/send
     @UsePipes(new ValidationPipe({ transform: true, whitelist: true })) // Enable validation using the DTO
     async sendSms(@Body() sendSmsDto: SendSmsDto) {
       this.logger.log(`Received request to send SMS: ${JSON.stringify(sendSmsDto)}`);
       try {
         const result = await this.smsService.sendSms(sendSmsDto.recipient, sendSmsDto.body);
         // Successfully sent (or at least accepted by MessageBird)
         return {
           message: 'SMS submitted successfully.',
           data: {
             messageId: result.id, // Or relevant data from the MessageBird response
             recipients: result.recipients.totalSentCount,
           },
         };
       } catch (error) {
         this.logger.error(`Error sending SMS: ${error.message}`, error.stack);
         // Throw standard HTTP exceptions
         throw new HttpException(
           `Failed to send SMS: ${error.message}`,
           HttpStatus.INTERNAL_SERVER_ERROR, // Or BAD_GATEWAY if it's clearly an external API issue
         );
       }
     }
   }
   
   • @Controller('sms'): Sets the base path for all routes in this controller to /sms.
   • @Post('send'): Defines a handler for POST requests to /sms/send.
   • @Body() sendSmsDto: SendSmsDto: Injects the validated request body into the sendSmsDto parameter.
   • @UsePipes(new ValidationPipe(...)): Automatically validates the incoming body against the SendSmsDto.
     • transform: true: Automatically transforms the incoming plain object to an instance of SendSmsDto.
     • whitelist: true: Strips any properties from the request body that are not defined in the DTO.
   • Error Handling: The try...catch block handles potential errors from the SmsService and throws an HttpException with an appropriate status code and message.

4. Update SmsModule: Add the SmsController to the controllers array in src/sms/sms.module.ts.

   typescript

   // src/sms/sms.module.ts
   import { Module } from '@nestjs/common';
   import { SmsService } from './sms.service';
   import { SmsController } from './sms.controller'; // Import the controller
   
   @Module({
     controllers: [SmsController], // Add the controller
     providers: [SmsService],
     exports: [SmsService],
   })
   export class SmsModule {}
   

5. Enable Validation Globally (Optional but Recommended): Instead of applying @UsePipes to every controller method, you can enable the ValidationPipe globally in src/main.ts.

   typescript

   // src/main.ts
   import { NestFactory } from '@nestjs/core';
   import { AppModule } from './app.module';
   import { Logger, ValidationPipe } from '@nestjs/common'; // Import ValidationPipe
   
   async function bootstrap() {
     const app = await NestFactory.create(AppModule);
     const logger = new Logger('Bootstrap'); // Create a logger instance
   
     // Enable global validation pipe
     app.useGlobalPipes(new ValidationPipe({
       transform: true, // Automatically transform payloads to DTO instances
       whitelist: true, // Strip properties not defined in DTO
       forbidNonWhitelisted: true, // Throw error if non-whitelisted properties are present
       transformOptions: {
         enableImplicitConversion: true, // Allow basic type conversions
       },
     }));
   
     // Configure global prefix (optional)
     // app.setGlobalPrefix('api/v1');
   
     const port = process.env.PORT || 3000;
     await app.listen(port);
     logger.log(`Application listening on port ${port}`);
     // Removed log related to /api documentation as Swagger setup is not included.
   }
   bootstrap();
   

   If you enable it globally, you can remove the @UsePipes(...) decorator from the SmsController.

5. Testing the API Endpoint

Let's verify our implementation.

1. Start the Application:

   bash

   npm run start:dev
   

   This starts the NestJS application in watch mode. Look for the log message indicating the port it's running on (usually 3000).

2. Send a Test Request (Using curl): Open a new terminal window and use curl (or a tool like Postman or Insomnia) to send a POST request. Replace YOUR_RECIPIENT_NUMBER with a valid phone number (use your own for testing with a live key, or any validly formatted number for a test key).

   bash

   curl -X POST http://localhost:3000/sms/send \
   -H ""Content-Type: application/json"" \
   -d '{
     ""recipient"": ""YOUR_RECIPIENT_NUMBER"",
     ""body"": ""Hello from my NestJS MessageBird App!""
   }'
   

3. Check Response:

   • Success: You should receive a JSON response similar to:

     json

     {
       ""message"": ""SMS submitted successfully."",
       ""data"": {
         ""messageId"": ""some-messagebird-message-id"",
         ""recipients"": 1
       }
     }
     

     Check your application console logs for success messages. If using a live key, check the recipient phone for the SMS. Check the MessageBird Dashboard logs (Logs -> Messages) to see the status.

   • Validation Error: If you send invalid data (e.g., missing body), you'll get a 400 Bad Request response detailing the errors:

     json

     {
       ""statusCode"": 400,
       ""message"": [
         ""Message body cannot be empty."",
         ""Message body must contain at least 1 character.""
       ],
       ""error"": ""Bad Request""
     }
     

   • API Error: If MessageBird rejects the request (e.g., invalid API key, insufficient balance, invalid originator), you'll get a 500 Internal Server Error (or the status code you configured in the controller's HttpException):

     json

     {
       ""statusCode"": 500,
       ""message"": ""Failed to send SMS: MessageBird API Error: Authentication failed""
     }
     

     Check your application console logs for detailed error messages from the SmsService.

6. Error Handling and Logging

We've already incorporated basic logging and error handling:

• NestJS Logger: Used in the service and controller to log informational messages and errors. Consider configuring log levels (e.g., only log errors in production) via environment variables or configuration files. You can also integrate more advanced logging libraries like Winston or Pino with NestJS.
• ValidationPipe: Handles input validation errors, returning 400 responses.
• try...catch + HttpException: Catches errors from the SmsService (including MessageBird API errors) and translates them into appropriate HTTP responses (e.g., 500 Internal Server Error, 502 Bad Gateway).
• MessageBird Error Structure: When the SDK rejects the promise, the err object often contains an errors array with more specific details from the MessageBird API (code, description, parameter). Logging JSON.stringify(err.errors) can be very helpful for debugging.

Retry Mechanisms (Advanced): For critical SMS, you might implement retries with exponential backoff, especially for transient network errors or temporary MessageBird API issues (e.g., rate limiting). Libraries like async-retry or NestJS scheduler features (@nestjs/schedule) could be used, but are beyond the scope of this basic guide. Be cautious not to retry indefinitely or for errors that won't resolve (like invalid credentials).

7. Security Considerations

• API Key Security:

  • Never commit API keys to version control (.env in .gitignore).
  • Use environment variables managed securely in your deployment environment (e.g., secrets management tools, platform environment variables).
  • Consider rotating API keys periodically.

• Input Validation: Already implemented using class-validator DTOs. This prevents malformed requests and basic injection attempts in the body parameters. Always validate and sanitize any user-provided input.

• Rate Limiting: Protect your API endpoint from abuse. Use @nestjs/throttler to limit the number of requests per IP address or user within a specific timeframe.

  bash

  npm install --save @nestjs/throttler
  

  Configure it in app.module.ts:

  typescript

  // src/app.module.ts
  import { ThrottlerModule, ThrottlerGuard } from '@nestjs/throttler';
  import { APP_GUARD } from '@nestjs/core'; // Import APP_GUARD
  import { Module } from '@nestjs/common';
  import { ConfigModule } from '@nestjs/config';
  import { AppController } from './app.controller';
  import { AppService } from './app.service';
  import { SmsModule } from './sms/sms.module';
  
  @Module({
    imports: [
      ConfigModule.forRoot({ isGlobal: true, envFilePath: '.env' }),
      ThrottlerModule.forRoot([{ // Configure rate limiting
        ttl: 60000, // Time window in milliseconds (e.g., 60 seconds)
        limit: 10,  // Max requests per window per IP
      }]),
      SmsModule,
    ],
    controllers: [AppController],
    providers: [
      AppService,
      { // Apply ThrottlerGuard globally
        provide: APP_GUARD,
        useClass: ThrottlerGuard,
      },
    ],
  })
  export class AppModule {}
  

• Authentication/Authorization: This guide assumes the API endpoint might be internal or protected by other means (e.g., API Gateway, firewall). For public-facing APIs, implement proper authentication (e.g., JWT, API Keys specific to your API consumers) to ensure only authorized clients can trigger SMS sending.

• Originator Restrictions: Be aware of country-specific regulations regarding Alphanumeric Sender IDs and ensure your chosen originator is compliant and approved.

8. Unit Testing the Service

NestJS encourages testing. Let's write a basic unit test for SmsService.

1. Open Test File: Navigate to src/sms/sms.service.spec.ts. The CLI generates a basic shell.

2. Write Unit Tests: Mock dependencies (ConfigService, messagebird SDK) and test the sendSms method logic.

   typescript

   // src/sms/sms.service.spec.ts
   import { Test, TestingModule } from '@nestjs/testing';
   import { SmsService } from './sms.service';
   import { ConfigService } from '@nestjs/config';
   // Logger is not explicitly needed for these tests, so it's removed from providers
   
   // Mock the messagebird library
   const mockMessageBirdCreate = jest.fn();
   const mockMessageBirdClient = {
     messages: {
       create: mockMessageBirdCreate,
     },
   };
   // Mock the require('messagebird') call
   jest.mock('messagebird', () => {
     // This mocks the function returned by require('messagebird')
     return jest.fn().mockImplementation(() => mockMessageBirdClient);
   }, { virtual: true }); // Use virtual mock for require
   
   describe('SmsService', () => {
     let service: SmsService;
     let configService: ConfigService;
   
     // Mock ConfigService values
     const mockConfigService = {
       get: jest.fn((key: string) => {
         if (key === 'MESSAGEBIRD_API_KEY') return 'test_api_key';
         if (key === 'MESSAGEBIRD_ORIGINATOR') return '+1234567890';
         return null;
       }),
     };
   
     beforeEach(async () => {
       // Reset mocks before each test
       mockMessageBirdCreate.mockClear();
       // Also clear mocks on the module factory itself if require was mocked
       (require('messagebird') as jest.Mock).mockClear();
   
       const module: TestingModule = await Test.createTestingModule({
         providers: [
           SmsService,
           {
             provide: ConfigService,
             useValue: mockConfigService, // Use the mock implementation
           },
           // Logger removed from providers as it's not directly injected/tested here
         ],
       }).compile();
   
       service = module.get<SmsService&gt;(SmsService);
       configService = module.get<ConfigService&gt;(ConfigService); // Get instance if needed for assertions
     });
   
     it('should be defined', () =&gt; {
       expect(service).toBeDefined();
     });
   
     describe('sendSms', () =&gt; {
       const recipient = '+9876543210';
       const body = 'Test message';
       const originator = '+1234567890'; // Expected from mockConfigService
   
       it('should call messagebird.messages.create with correct parameters and resolve on success', async () =&gt; {
         const mockResponse = { id: 'mock-message-id', recipients: { totalSentCount: 1 } };
         // Configure the mock implementation for the SDK call for this test
         mockMessageBirdCreate.mockImplementation((params, callback) =&gt; {
            callback(null, mockResponse); // Simulate success
         });
   
         await expect(service.sendSms(recipient, body)).resolves.toEqual(mockResponse);
   
         expect(mockMessageBirdCreate).toHaveBeenCalledTimes(1);
         expect(mockMessageBirdCreate).toHaveBeenCalledWith(
           {
             originator: originator,
             recipients: [recipient],
             body: body,
           },
           expect.any(Function), // The callback function
         );
       });
   
       it('should reject with an error if messagebird.messages.create fails', async () =&gt; {
         const mockError = {
            message: ""API Error"", // Corrected quotes
            errors: [{ code: 2, description: 'Request parameter validation failed', parameter: 'recipients' }]
         };
         // Configure the mock implementation for the SDK call for this test
         mockMessageBirdCreate.mockImplementation((params, callback) =&gt; {
            callback(mockError, null); // Simulate error
         });
   
         await expect(service.sendSms(recipient, body)).rejects.toThrow(
            `MessageBird API Error: ${JSON.stringify(mockError.errors)}` // Check for the formatted error
         );
   
         expect(mockMessageBirdCreate).toHaveBeenCalledTimes(1);
          expect(mockMessageBirdCreate).toHaveBeenCalledWith(
           {
             originator: originator,
             recipients: [recipient],
             body: body,
           },
           expect.any(Function),
         );
       });
   
        it('should throw an error during initialization if API key is missing', async () =&gt; {
            // Override config mock for this specific scenario
            const missingKeyConfig = {
               get: jest.fn((key: string) =&gt; {
                    if (key === 'MESSAGEBIRD_ORIGINATOR') return '+1234567890';
                    return null; // Simulate missing API key
                })
            };
   
            // We need to test the module compilation which triggers the constructor
            await expect(Test.createTestingModule({
                providers: [
                    SmsService,
                    { provide: ConfigService, useValue: missingKeyConfig },
                    // Logger not needed here either
                ],
            }).compile()).rejects.toThrow('MessageBird environment variables missing.');
        });
     });
   });
   
   • Mocking: We use jest.fn() and jest.mock to create mock implementations of ConfigService and the messagebird SDK.
   • Test Cases: We test the successful path, the error path, and the constructor initialization error handling.
   • Logger: Logger has been removed from the test module providers for cleanliness, as it wasn't actively used in the tests.

3. Run Tests:

   bash

   npm run test
   

   Or for a specific file:

   bash

   npm run test -- src/sms/sms.service.spec.ts
   

9. Troubleshooting and Caveats

• Error: Authentication failed: Double-check your MESSAGEBIRD_API_KEY in .env. Ensure you're using the correct key (live vs. test) and that it hasn't been revoked. Verify there are no typos or extra spaces.
• Error: message could not be sent because the originator is invalid: Ensure MESSAGEBIRD_ORIGINATOR in .env matches a purchased number or a registered and approved Alphanumeric Sender ID in your MessageBird account. Check country restrictions for Alphanumeric Sender IDs.
• Error: Request parameter validation failed (Parameter: recipients): Ensure the recipient number is in a valid format. While MessageBird is somewhat flexible, E.164 format (+ followed by country code and number, e.g., +14155552671) is strongly recommended. The SDK expects recipients as an array.
• Error: No (suitable) routes found: You might have insufficient balance (for live keys) or the recipient country/network might not be supported by your MessageBird account setup or the originator type. Check your balance and MessageBird's coverage documentation.
• SMS Not Received (Live Key):
  • Verify recipient number is correct and has signal.
  • Check MessageBird Dashboard Logs for detailed delivery status (e.g., ""delivered"", ""failed"", ""expired"").
  • Ensure the number isn't on a Do-Not-Disturb list or blocked by the carrier.
  • Check for country-specific regulations or carrier filtering.
• Callback vs. Promise: Remember the base MessageBird Node SDK uses callbacks. Our Promise wrapper is crucial for clean async/await usage in NestJS. Errors in the promise handling logic can mask SDK errors.
• Rate Limits: MessageBird imposes API rate limits. If sending high volumes, check their documentation and implement appropriate delays or throttling in your application. The ThrottlerModule helps protect your endpoint, but doesn't manage MessageBird's API limits directly.
• SDK Version: Ensure you are using a reasonably recent version of the messagebird package, as APIs and methods can change.

10. Deployment and CI/CD

• Build: Create a production build:

  bash

  npm run build
  

  This compiles TypeScript to JavaScript in the dist folder.

• Run Production: Start the application using Node.js directly on the compiled output:

  bash

  node dist/main
  

• Environment Variables: Ensure your production environment (e.g., Docker container, PaaS like Heroku/Vercel/AWS Elastic Beanstalk, VM) has the MESSAGEBIRD_API_KEY and MESSAGEBIRD_ORIGINATOR environment variables set securely. Do not include the .env file in your production artifact; use the platform's mechanism for environment variables.

• CI/CD Pipeline: Set up a pipeline (e.g., GitHub Actions, GitLab CI, Jenkins) to:

  • Install dependencies (npm ci recommended for consistency).
  • Lint and format code.
  • Run tests (npm run test).
  • Build the application (npm run build).
  • Deploy the dist folder, node_modules, package.json, and any other necessary files (like .env.production if used, though platform env vars are better) to your hosting environment.

• Process Management: Use a process manager like pm2 or rely on your platform's built-in service management (e.g., systemd, Docker orchestration) to keep the Node.js application running reliably, handle restarts, and manage logs.