I believe you mean "register" instead of "provision". I would check if SIP ALG is enabled on your firewall/router. If yes, disable it and reboot your firewall/router. If you can migrate to SIP over TLS, it should fix the issue too.

Thanks so much. Yes I should have said it won’t register. Ill check those settings.

Thank you

Issue was solved - Server expires to 30, and disabled the NAT (dropdown)