Anyone have any experience setting up freePBX behind the Ubiquiti Dream Machine Pro

Hello, I have a UDM installed as primary (and only) router configuration. I also have a FreePBX running a few voip phones. However since installing the UDM the PBX now refuses to register its trunk with voip.ms

I've checked firewall settings and port forwarding. everything seems as it should be. Not to mention, the other routers that we tested didn't need any configuration to work. Is this a known quirk with Ubiquiti? Any ideas what might be holding me up?