The system just disconnects the call. When using an internal number calling ext 702 (which forwards to an external number) it connects, no problem. When a call comes in on the SIP Trunk, forwarding to 702 (I need this for our IVR / Digital Receptionist) the call fails. It appears to be related as to how 3cx handles the call to the SIP Trunk. 02/16/2017 4:07:50 PM - L:129.6[Line:10000>>1866xxxxxxx] got Failure: Failure Recv 500/INVITE from 18.104.22.168:5060 tid=781853790f4cfa29 Call-ID=x-bbNT07vdcp0qYC7cEYmg..: SIP/2.0 500 Body-less INVITE is not supported As per the error above it appears that the transferred call is missing the body. Any idea's?