21666: 'FallbackFrom' requires MessagingServiceSid

The FallbackFrom parameter requires a MessagingServiceSid to be provided. FallbackFrom specifies the SMS/MMS sender to use when RCS delivery fails, which requires a Messaging Service with an RCS Sender in its sender pool.

• FallbackFrom was specified without a MessagingServiceSid in the request.

• Add a MessagingServiceSid to your request. The Messaging Service must have at least one RCS Sender in its sender pool.
• If you did not mean to use RCS, remove FallbackFrom and use the From parameter to send SMS/MMS directly.