Hi All, I'm having some major issues for the last few days on my customers 3CX system. Originally I had the license bug, which I was told to upgrade to the latest version, which resolve that, but I'm now getting calls drop every 30 seconds, to an issue with my firewall. I have spoken to the Router/Firewall tech support (Zyxel) and they have confirmed SIP ALG is disabled and that the firewall is now 100% open, however, 3CX is still throwing up the ACK error. I have now been told to re-enable STUN, which I have done. I've tried again, run a wireshark capture, to no avail. I am now awaiting 3CX tech support response. This is absolutely ridiculous, I can't resell 3CX if it's going to have a serious problem like this, my customer has had no phone system now since Thursday, that's 6 days! The call quality is fine, no issues there, but as soon as you hit 30 seconds, the call drops! This has all come about due to them recommending I upgrade, due to the license issue. - So surely it's a 3CX issue? Has anyone else had this?