I am attempting to setup 3CX 15 Debian to work with our SIP provider (not officially supported, but standard SIP connections) and can't seem to get the Outbound Parameters to override the registration. When the registration sends, the to: field looks like the first line but should look like the second line (dummy data). Wrong - To: <sip:firstname.lastname@example.org:5100> Right - To: <sip:email@example.com> I have the To: User Part and To: Host Part set with custom values in Outbound Parameters, but nothing I do changes the actual registration. Is there a known bug that prevents this? Do I need to modify something else? EDIT: I believe the issue is that the registration headers aren't updated. Does anyone know a way to modify the registration headers like you can the Invite headers?