21609: Invalid 'StatusCallback'

Twilio returns this error when the StatusCallback URL you provided is not a valid URL.

• The StatusCallback value is not a valid URL.
• The URL exceeds the 4000-character limit.
• The URL is missing one or more components of a fully qualified URL (protocol, hostname, file path, or properly URL‑encoded query parameters).
• The URL is not reachable by Twilio over the public internet.
• The URL's hostname is invalid (for example, contains underscores), which violates the Messages API StatusCallback parameter requirements.

• Submit a fully qualified URL that includes all of the following: protocol (http:// or https://), hostname, file path, and properly URL‑encoded query parameters.
• Ensure the URL length doesn't exceed 4000 characters.
• Ensure Twilio can reach the StatusCallback URL over the public internet.
• Ensure the URL contains a valid hostname; underscores are not permitted for the Messages API StatusCallback parameter.

• Messages resource
• Track the Message Status of Outbound Messages