# 21666: 'FallbackFrom' requires MessagingServiceSid

Log Type: APPLICATION

Log Level: ERROR

## Description

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.

### Possible causes

* `FallbackFrom` was specified without a `MessagingServiceSid` in the request.

### Possible solutions

* 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.