Stabilize FreePBX Trunk Registration

I recently migrated our phone system from Issabel to FreePBX, and the new setup is proving unreliable. The core problem is configuration-related: trunks refuse to register, so inbound and outbound calls drop out entirely. I have already confirmed that the SIP credentials and server details are correct on the provider side, which leads me to believe the fault sits within the FreePBX trunk settings themselves (likely PJSIP vs. Chan-SIP handling, authentication parameters, or NAT/transport details).

Your task is to review the current FreePBX configuration, identify why the trunks fail to register, and implement a stable fix. I can provide SSH and GUI access along with CLI logs showing the repeated registration attempts. Once working, the trunks must stay registered for at least 24 hours without manual intervention or unexpected reloads.

Deliverables (acceptance criteria)
• Corrected trunk configuration that registers successfully and survives reloads/reboots
• Clean Asterisk log with no registration errors or flapping events for 24 h
• Brief change log explaining what was modified so I can replicate it on a standby server

If you are comfortable navigating FreePBX, Asterisk CLI, and SIP debugging tools such as sngrep or tcpdump, this should be a quick engagement.