CTMApexTextMessage.cls

public class CTMApexTextMessage {
  // Your api keys from account settings
  private static String apiKey() { return 'your-api-key'; }
  private static String apiSec() { return 'your-api-sec'; }
  private static String apiHost() { return 'api.calltrackingmetrics.com'; }
  private static String apiAccount() { return 'your-account-id'; }
  private static String apiAuthorization() { 
    return 'Basic ' + EncodingUtil.base64Encode(Blob.valueOf(apiKey() + ':' + apiSec()));
  }
  
  @InvocableMethod(label='Send Text Message')
  public static CTMTextMessageOutput[] sendTextMessage(List<CTMTextMessageInput> inputs) {
    List<CTMTextMessageOutput> outputs = new List<CTMTextMessageOutput>();

    for (CTMTextMessageInput input : inputs) {
      CTMTextMessageOutput output = new CTMTextMessageOutput();

      try {
        String recordId = input.recordId;
        String phoneNumber = input.phoneNumber;
        String message = input.message;

        output.recordId = recordId;

        // Enqueue the future method to perform the callout
        sendMessage(recordId, phoneNumber, message);

        output.success = true; // Assume success since callout is asynchronous
        output.message = 'Text message sent asynchronously';
        outputs.add(output);
      } catch (Exception e) {
        output.message = e.getMessage();
        output.success = false;
        outputs.add(output);
      }
    }

    // You can handle the outputs list as required
    System.debug(outputs);
    return outputs;
  }
  
  @future(callout=true)
  public static void sendMessage(String recordId, String phone, String message) {
    Http http         = new Http();
    HttpRequest req   = prepareRequest(recordId, phone, message);

    http.send(req);
  }
  public static String endpoint() {
     return 'https://' + apiHost() + '/api/v1/accounts/' + apiAccount() + '/sms';
  }
  public static HttpRequest prepareRequest(String Id, String phone, String message) {
    Map<String, String> payload = new Map<String, String>();
    payload.put('salesforce_id', Id);
    payload.put('to', phone);
    payload.put('from', '+19542895725');
    payload.put('msg', message);

    HttpRequest req   = new HttpRequest();
    String url = endpoint();
    req.setEndpoint(url);
    req.setHeader('Content-Type','application/json');        
    req.setHeader('Authorization',apiAuthorization());        
    req.setMethod('POST');
    req.setBody(JSON.serialize(payload));
    return req;
  }
  
  public class CTMTextMessageInput {
    @InvocableVariable(required=true)
    public String recordId;
  
    @InvocableVariable(required=true)
    public String phoneNumber;
  
    @InvocableVariable(required=true)
    public String message;
  }
  
  public class CTMTextMessageOutput {
    @InvocableVariable
    public String recordId;
  
    @InvocableVariable
    public Boolean success;
  
    @InvocableVariable
    public String message;
  }
}

CTMApexTextMessageMock.cls

@isTest
public class CTMApexTextMessageTest {
    @isTest
    static void testSendTextMessage() {
        // Setup
        CTMApexTextMessage.CTMTextMessageInput input = new CTMApexTextMessage.CTMTextMessageInput();
        input.recordId = '001xx000003DGb3AAG';
        input.phoneNumber = '+1234567890';
        input.message = 'Test message';

        List<CTMApexTextMessage.CTMTextMessageInput> inputs = new List<CTMApexTextMessage.CTMTextMessageInput>{ input };

        // Mock HTTP Callout
        Test.setMock(HttpCalloutMock.class, new CTMApexTextMessageMock());

        // Test
        Test.startTest();
        List<CTMApexTextMessage.CTMTextMessageOutput> outputs = CTMApexTextMessage.sendTextMessage(inputs);
        Test.stopTest();

        // Assertions
        System.assertEquals(1, outputs.size());
        CTMApexTextMessage.CTMTextMessageOutput output = outputs[0];
        System.assertEquals('001xx000003DGb3AAG', output.recordId);
        System.assertEquals(true, output.success);
        System.assertEquals('Text message sent asynchronously', output.message);
    }
}

// Mock implementation of HttpCalloutMock
public class CTMApexTextMessageMock implements HttpCalloutMock {
    public HTTPResponse respond(HttpRequest req) {
        HttpResponse res = new HttpResponse();
        res.setHeader('Content-Type', 'application/json');
        res.setBody('{"success":true}');
        res.setStatusCode(200);
        return res;
    }
}