Balance 210 NAT-PmP failing

This one is a little more complicated. It is an HA of Balance 210’s and that seems to be fine. The Peplink is sending SIP traffic to an HA PBX cluster. We enabled NAT-PmP so that the port it sends traffic outbound matches what the PBX expects it to be.

What is happening is that the Peplink is nating the port and the carrier refuses to accept it from the nat’ed port according to them. I’m low on ideas on how to get the devices to behave, so help would be much appreciated.