IPcomms FBPX and Snom compatibility issue with INVITE


I have a problem with SNOM 320 phone. The phone registers with PBX using line parameter:

Contact: <sip:[email protected]:5060;line=mptvmknr>;q=1.0;+sip.instance=“urn:uuid:34390545-3290-46db-b3b0-91397b148c28”;audio;mobility=“fixed”;duplex=“full”;description=“snom320”;actor=“principal”;events=“dialog”;methods=“INVITE,ACK,CANCEL,BYE,REFER,OPTIONS,NOTIFY,SUBSCRIBE,PRACK,MESSAGE,INFO”

And I can make outgoing calls. NAT is configured properly.
However, I cannot receive incoming calls from IPComms server because the INVITE message comes without the line parameter and gets 404 error.

INVITE sip:[email protected]:5060 SIP/2.0

How is it possible to configure the trunk in the PBX to force it to use the line parameter?

For some reason PBX ignores it when routing the call.

User-Agent: FPBX-2.9.0(
Asterisk PBX

Thank you in advance. I am the first time in this forum so hope that I add this request in the right place…