I can't get my remote extension to connect. The 3CX soft phone connects fine. The SPA504G is setup the same as Kevin explains in the remote video. Packet size: .020, stun enabled, stun server: stun2.3cx.com (same as server), EXT 1 setup with public IP in proxy, user id, p/w, auth enabled, auth pin and resync time set to 300 seconds. The buttons light up and show the extension with a dial tone, but pressing any button gets a fast busy. The phone status shows either Registration State: Failed403 or Registration State: FailedNo Response. The firewall should be set correctly with 5060, 5090 and 9000-9049 forwarded using the correct protocols, plus the soft phone works. Any ideas?