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Twilio Error 21421

The 'To' phone number is not currently reachable via SMS.

Understanding Twilio: A Powerful SMS Communication API

Twilio is a cloud communications platform that enables developers to programmatically send and receive SMS messages, make and receive phone calls, and perform other communication functions using its web service APIs. It is widely used in applications for customer engagement, notifications, and two-factor authentication.

Identifying the Symptom: Error 21421

When using Twilio's SMS API, you might encounter the error code 21421. This error indicates that the 'To' phone number is not currently reachable via SMS. This can be a common issue when sending messages to recipients who may have network issues or incorrect phone numbers.

Exploring the Issue: What Does Error 21421 Mean?

Error 21421 is a specific error code returned by Twilio when an SMS message cannot be delivered to the intended recipient. This typically occurs when the recipient's phone number is either incorrect, inactive, or not capable of receiving SMS messages at the time of sending.

Possible Causes of Error 21421

  • The recipient's phone number is incorrect or formatted improperly.
  • The recipient's phone is turned off or out of network coverage.
  • The recipient's phone number is not SMS-enabled.

Steps to Resolve Error 21421

To resolve this issue, follow these actionable steps:

1. Verify the Recipient's Phone Number

Ensure that the phone number is correct and formatted according to the E.164 standard. This format includes the country code, area code, and the local number.

2. Check Network Coverage

Contact the recipient to confirm that their phone is turned on and within network coverage. You can also use Twilio's Lookup API to check the phone number's status.

3. Ensure SMS Capability

Verify that the recipient's phone number is capable of receiving SMS messages. Some numbers, such as landlines, may not be SMS-enabled.

Additional Resources

For more information on handling Twilio errors, visit the Twilio Error Code Documentation. You can also explore the Twilio SMS API Documentation for further guidance on sending messages.

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