Hello, thanks for your help.
I attach the whole INVITE message
INVITE sip:+393922568003@ims.example.net;user=phone SIP/2.0 Via: SIP/2.0/TCP 10.139.140.249:5260;branch=z9hG4bK+183a8f199afae25013ec3da9c768d7e71+sip+1+a64ef5ee From: "Flavio" sip:+393891524510@ims.example.net;tag=10.139.140.249+1+6a272b5b+75130025 To: sip:+393922568003@ims.example.net CSeq: 1 INVITE Expires: 180 Route: sip:orig@scscf.ims.example.net:7060;lr Content-Length: 250 Call-Info: sip:10.139.140.249:5260;method="NOTIFY;Event=telephone-event;Duration=2000" Supported: replaces P-Charging-Vector: icid-value=070d4ad6d2ad162b8aa5bb701dbca1f5 Contact: sip:+393891524510@10.139.246.113:32734 Record-Route: sip:10.139.140.249:5260;transport=tcp;lr Content-Type: application/sdp P-Served-User: sip:+393891524510@ims.example.net P-Asserted-Identity: sip:+393891524510@ims.example.net Max-Forwards: 69 Call-ID: 0gQAAC8WAAACBAAALxYAAHDXeTpfsrd8TbexIcx32VhAZNOydD+L9Uama1JAimxtSDPFHcDNu7JpFnHKPNLfKQ--@10.139.140.249 Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE, SUBSCRIBE, INFO User-Agent: X-Lite release 4.5.5 stamp 71236 P-Visited-Network-ID: sbc1.stage.ims.example.net Accept: application/sdp, application/dtmf-relay