Twilio Error 21606

The 'From' number is not a valid, SMS-capable number.

Understanding Twilio and Its Purpose

Twilio is a cloud communications platform that enables developers to build, scale, and operate real-time communications within their software applications. It provides APIs for SMS, voice, video, and other communication channels, making it a versatile tool for integrating communication capabilities into applications.

Identifying the Symptom: Error 21606

When working with Twilio's SMS API, you might encounter the error code 21606. This error typically manifests when attempting to send an SMS message, and the operation fails with a message indicating that the 'From' number is not valid or SMS-capable.

Exploring the Issue: What is Error 21606?

Error 21606 is triggered when the 'From' number specified in your API request is not a valid, SMS-capable number. This means that the number either does not belong to Twilio or is not configured to send SMS messages. Twilio requires that the 'From' number be a Twilio number that supports SMS to ensure compliance and proper message routing.

Why This Error Occurs

The primary reason for this error is using a number that is not provisioned by Twilio or one that does not have SMS capabilities. This can happen if the number is a voice-only number or if it is not owned by your Twilio account.

Steps to Fix Error 21606

To resolve this issue, follow these steps:

1. Verify the 'From' Number

  • Log in to your Twilio Console.
  • Navigate to the Phone Numbers section.
  • Check that the 'From' number you are using is listed under your active Twilio numbers.
  • Ensure that the number is SMS-capable. You can verify this by checking the capabilities listed for the number in the console.

2. Update Your API Request

  • In your application code, update the 'From' number in your API request to a valid Twilio number that supports SMS.
  • Example API request format:
    {
    "From": "+1234567890", // Replace with your Twilio number
    "To": "+0987654321",
    "Body": "Hello, this is a test message!"
    }

3. Purchase a New SMS-Capable Number

  • If you do not have an SMS-capable number, you can purchase one from the Twilio Console.
  • Go to the Phone Numbers Search page.
  • Select a number that supports SMS and add it to your account.

Conclusion

By ensuring that your 'From' number is a valid, SMS-capable Twilio number, you can effectively resolve Error 21606 and ensure smooth SMS communication through your application. For more detailed information, refer to the Twilio SMS Documentation.

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