NAT’ing. Using an alternate port requires planning. Not all FreePBX users (me included) have the skills or experience to do so. I recently saw a post where OP seems to have issues with non standard ports as well.
I will search the internet on how to activate the logs for sip debugging.
I checked my router and found some mistakes by me.
I set for example 6666 --> 5061 in port forwarding.
Some how that does not work. Then I set 5061 --> 5061 and it works.
Next tried setting the sip tls port in sip setting page in freepbx to 6666 and change back the router to 6666 --> 6666. But does not work even after restarting the freepbx server.
Please note the firewall is off.
So finally the router is set to 5061…
If you can write something in the FreePBX Documentation Center will be nice. https://wiki.freepbx.org/display/FDT/FreePBX+Security+Best+Practices