thank you @Stewart1 for your reply, I have edited the outbound proxy as you suggest, but I didn’t understand where to place in my configuration the srvmi.p.ims.tiscali.net . Anyway now the error is different, I’m receiving the following
[2019-10-04 08:06:19] WARNING[1807]: res_pjsip_outbound_registration.c:993 handle_registration_response: 403 Forbidden fatal response received from 'sip:ims.tiscali.net:5060' on registration attempt to 'sip:0039XXXXXXXXXX@ims.tiscali.net:5060', retrying in '10' seconds
<--- Transmitting SIP request (623 bytes) to UDP:213.205.21.8:5060 --->
REGISTER sip:core1.p.ims.tiscali.net:5060 SIP/2.0
Via: SIP/2.0/UDP 82.84.72.XX:5060;rport;branch=z9hG4bKPje8eeb917-0188-4f0b-ac17-e85c305a3f13
From: <sip:0039XXXXXXXXXX@ims.tiscali.net>;tag=d48ea4b8-88b1-49fd-8944-c5e79b57d735
To: <sip:0039XXXXXXXXXX@ims.tiscali.net>
Call-ID: e4462ce5-b0b2-4d17-8df0-fcbbe2506ae9
CSeq: 20364 REGISTER
Contact: <sip:s@82.84.72.33:5060;line=qzyzcgz>
Expires: 3600
Allow: OPTIONS, SUBSCRIBE, NOTIFY, PUBLISH, INVITE, ACK, BYE, CANCEL, UPDATE, PRACK, REGISTER, REFER, MESSAGE
Route: <sip:ims.tiscali.net:5060>
Max-Forwards: 70
User-Agent: FPBX-14.0.13.4(13.26.0)
Content-Length: 0
<--- Transmitting SIP request (503 bytes) to UDP:213.205.21.8:5060 --->
OPTIONS sip:core1.p.ims.tiscali.net:5060 SIP/2.0
Via: SIP/2.0/UDP 82.84.72.XX:5060;rport;branch=z9hG4bKPjcc61d4dc-1c5f-4dcc-85b9-61bb5a85ef70
From: <sip:0039XXXXXXXXXX@192.168.1.99>;tag=a30fc92e-c57b-412f-89a1-4d33c42dfc86
To: <sip:0039XXXXXXXXXX@ims.tiscali.net>
Contact: <sip:0039XXXXXXXXXX@82.84.72.33:5060>
Call-ID: 67701b88-74d2-40b9-9e53-13af39265a99
CSeq: 20100 OPTIONS
Route: <sip:0039XXXXXXXXXX@ims.tiscali.net:5060>
Max-Forwards: 70
User-Agent: FPBX-14.0.13.4(13.26.0)
Content-Length: 0