Sangoma support was finally able to get things working but it took them several hours. We had to configure the phone locally first and then send it out into the wild after it had configured locally. I’m not sure what all they did because they were doing it but a few days later, they got it to work.
It was much harder than I’d expected and if I had to add another one, I don’t know how to do it because I don’t know what they finally ended up doing to make it work.