Yeah that's likely it. The audio stream comes from a different IP that the VOIPo server you are connected to so some routers don't "link" the two together and block it.

We recommend setting a static IP in the router for the adapter and forwarding ports 5000-65000 (UDP) to the adapter.

If your router has SIP ALG, you also want to disable that.

This combo should resolve your issue. If you need any help with doing it, just give us a call.