I know that this has been aired before but I can’t see anything which helps so I thought it would be worth asking again.
My configuration is SIP Phone (POTS on Grandstream HT503) -> Asterisk 11.10.0 -> IAX trunk -> Asterisk -> SIP (another HT503 with outgoing Line).
If I use the phone locally directly to the SIP line then DTMF works phone to any IVR system.
When I bridge over IAX the remote end is reporting that the DTMF is being received but it obviously is not passing it out as the IVR goes back to the same options.
I have dtmfmode=rfc8233 on both SIP and IAX.
Any advice would be appreciated