UniFi VoIP: No Sound on Phone Call

The problem

The PBX is 3CX on a remote server with a public, static IP address. The 3CX PBX was originally configured and working properly befora using unifi solution.

Local and remove UVPs make and receive calls to/from external numbers and remote UVPs have no audio.

Solution

Make sure you have the option PBX delivers audio enabled:

Solution to Unifi Vo-IP problem