I have a situation here where when I send a INVITE to some specific user-agents in my environment I must change the fr_timer to a value lower than the default.

I can acomplish this using the "t_set_fr" commands in my cfg file, and it works like a charm.

The point is that when the timer reaches its limit, the kamailio server sends a CANCEL message to the user-agent. I know that this is the normal behavior, but I want to add the Reason field on it, so the user-agent application can know that the call wasn't answered on time.

I was looking the TM module documentation to understand how to do this, but I couldn't figure out a way to get this working.

Is there a way to add the Reason in CANCEL messages generated by the fr_timer?

Thanks.