Hello, I was already searching the forum for this issue, I noticed similar issues were reported before but I could not get the solution yet.... 3CX Phone for windows (latest version) works perfectly fine while inside the local network, but it wont work over L2TP VPN connection (zyxell firewall). I run firewall checker, results are all OK. I have static NAT enabled with 5060 and 5090 on my zyxel firewall. 3CX phone register over the L2TP VPN, says "on hook" and it dials a number no problem but no sounds is heard. If I dial *777 I can hear the central repeating what I said. If I however connect with SSTP VPN connection all is working perfectly (dialing, sound all is good). I just cannot figure out why there is not sound with L2TP VPN (hosted on zyxel) and also how it is possible to have the *777 test to be successful but the sound is missing on the actual call. 3CX central is connected with PATTON device to PSTN network. Any help appreciated. thank you!