I hope someone can help. I have a sip trunk from cucm 9.1 to a 3rd party PBX vendor. Calls between the CUCM and PBX works well, but if the PBX tries to transfer the an "internal PBX call" to me. I get no speach.
If you look at the CUCM trace you see the transfer coming in as an sip invite with a replace in the body, CUCM then sends a trying and immediateky after that a 403 forbidden.