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Twilio is a leading cloud communications platform that enables developers to programmatically send and receive text messages, make and receive phone calls, and perform other communication functions using its web service APIs. It is widely used for integrating SMS capabilities into applications, making it a popular choice for businesses looking to enhance their communication strategies.
When using Twilio's SMS API, you might encounter the error code 21409. This error typically manifests when attempting to send an SMS to a recipient's phone number that is not recognized as a valid VoIP number. As a result, the message fails to send, and you receive an error notification.
Error 21409 indicates that the 'To' phone number provided in your API request is not a valid VoIP number. Twilio requires that certain numbers, especially those used for specific types of messaging, be valid VoIP numbers to ensure proper routing and delivery of messages.
This error can occur if the phone number is incorrectly formatted, not registered as a VoIP number, or if there is a mismatch in the expected number type.
To resolve this issue, follow these actionable steps:
Ensure that the phone number you are using is correctly formatted and is indeed a VoIP number. You can use Twilio's Phone Number Lookup API to verify the type of the phone number.
curl -X GET 'https://lookups.twilio.com/v1/PhoneNumbers/{PhoneNumber}?Type=carrier' \
--user 'ACXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX:your_auth_token'
Confirm that the number is registered as a VoIP number. If it is not, you may need to contact the service provider or use a different number that is VoIP-enabled.
Once you have verified and confirmed the number, update your application to use the correct VoIP number. Ensure that your code reflects this change to avoid future errors.
For more information on handling Twilio errors, refer to the Twilio API Error Documentation. Additionally, you can explore the Twilio SMS API Documentation for comprehensive guidance on using Twilio's SMS services effectively.
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