I don’t think it was the DDNS. Mine is still set to off. There is a deployment number in the DDNS info box that was put there during installation.
I am using Endpoint Manager for the Sangoma phones as it’s required (but free for Sangoma phones). In the Endpoint Manager template I have the SIP Destination address set to external with a FQDN listed. We had tried using an IP but were having no success. We went to a FQDN as part of our efforts to get it to work. I don’t know if that’s actually needed as that wasn’t what allowed it to work but with over 100 hours invested in trying to get a Sangoma phone to register with a Sangoma appliance I wasn’t about to start undoing things to figure out what finally made it work. Of course I dread trying to do it again because I’m not sure what we finally stumbled over to make it work.
Provisioning Protocal is HTTPS (I think it’s important that this matches what you show in the Portal IP/FQDN protocol).