21655: The ContentSid is Invalid

This error means the ContentSid in your message request is not a valid Content Template SID for the message you are sending. Use a valid Content Template SID that matches the HX pattern and belongs to the same account that is creating the Message resource.

• The ContentSid value has a typo, is incomplete, or does not match the required ^HX[0-9a-fA-F]{32}$ format.
• The template was deleted, so the SID no longer points to an active Content Template.
• The template belongs to a different account or subaccount than the one used to create the message. A Content Sid can only be used by one Twilio account SID, and the Message resource is created under the account in your request.

• Copy the ContentSid directly from the Content Template Builder or from the Content API response. Confirm that it starts with HX and is 34 characters long.
• Verify that the template still exists by fetching it with GET /v1/Content/{ContentSid} or by listing templates with GET /v1/Content. If the template was deleted, create a new template and update your request to use the new SID.
• Send the message from the same account or subaccount that owns the template. If you authenticate the request with a different account, use a ContentSid created under that account instead.

• Send templates created with the Content Template Builder
• Content API public endpoints
• FAQs and Troubleshooting