Twilio Error 21411 encountered when sending an SMS.

The 'To' phone number is not a valid toll-free number.

Resolving Twilio Error 21411: Invalid Toll-Free Number

Understanding Twilio and Its Purpose

Twilio is a cloud communications platform that enables developers to programmatically send and receive SMS, make and receive phone calls, and perform other communication functions using its web service APIs. It is widely used in applications that require reliable and scalable communication solutions.

Identifying the Symptom: Error 21411

When using Twilio's SMS API, you might encounter the error code 21411. This error indicates that there is an issue with the phone number you are trying to send an SMS to.

What You Observe

While attempting to send an SMS, the operation fails, and you receive an error message stating: "The 'To' phone number is not a valid toll-free number."

Explaining the Issue: Error Code 21411

Error 21411 occurs when the 'To' phone number provided in your API request is not recognized as a valid toll-free number. Twilio requires that toll-free numbers adhere to specific formats and regulations.

Why This Happens

This error is typically caused by formatting issues or using a number that is not registered as toll-free. Toll-free numbers usually start with specific prefixes like 800, 888, 877, 866, 855, 844, or 833 in the United States.

Steps to Fix the Issue

To resolve Error 21411, follow these steps:

Step 1: Verify the Phone Number

  • Ensure that the phone number you are using is indeed a toll-free number.
  • Check the number's format and ensure it includes the correct country code and prefix.

Step 2: Use Twilio's Lookup API

Twilio provides a Lookup API to verify phone numbers. Use this API to confirm that the number is valid and toll-free:

curl -X GET 'https://lookups.twilio.com/v1/PhoneNumbers/{PhoneNumber}?Type=carrier' \
--user 'ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:your_auth_token'

Step 3: Correct the Number Format

  • If the number is incorrectly formatted, adjust it to meet the standard toll-free format.
  • Ensure the number includes the correct country code, e.g., +1 for the United States.

Additional Resources

For more information on handling Twilio errors, visit the Twilio API Errors Documentation. To learn more about toll-free numbers, check out the Twilio Toll-Free Numbers Guide.

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