21703: The Messaging Service does not have a phone number available to send a message

You have phone numbers or short codes in your Messaging Service, but none of them are capable of sending the requested message or media to this recipient. Possible causes vary depending on the type of message and the country of the destination number. Below are several common causes of this error.

• You attempted to send a message to a United States or Canada mobile number, but you do not have any US/Canada numbers or short codes in your Messaging Service. US/Canada mobile numbers are not reachable from Twilio numbers from outside the US/Canada, due to limitations imposed by carriers.**

• You only have a short code number in your Messaging Service, and the recipient is not reachable from your short code (for example, the To number is from a different country than your short code, or is on a carrier that does not support short code messaging).

• You attempted to send an MMS message, but you do not have any US/Canada long code numbers or an MMS-enabled short code in your Messaging Service.**

• You only have an Alphanumeric Sender ID in your Messaging Service, and the To number is in a country where Alphanumeric Sender ID is unsupported.

• You attempted to send a message to a United States mobile number, but you do not have any 10DLC numbers that are registered with a verified A2P Campaign in the Messaging Service. Only numbers registered with a verified A2P Campaign can be allowed to send to US based numbers.

** If you have recently added the number to a Messaging Service and while the number has a "Pending Registration" status, you may be experiencing a known issue which disables the ability to benefit from a temporary exception Twilio has made available to sending messages from "Pending Registration" numbers. You can reattempt to send from the impacted number by including the number in the "From" parameter of your API request instead of using the Messaging Service SID. However, this exception will sunset in the coming weeks. For more information about the 21703 error in relation to numbers "Pending Registration", and processing times to complete the Number Registration going forward, please review updated A2P 10DLC Number Registration Best Practices. To check the status of your numbers at any given time, you can use the Number Registration CSV report as described in How do I check that I have completed US A2P 10DLC registration.

Add a sender to your Messaging Service with the required capabilities, using the Twilio Console or the REST API.