Running 3CX V14 with SP3. system has been working fine until yesterday AM, outbound calls fail with "internal server error" I found no obvious issues on my end and firewall checker still passes all tests. Contacted my SIP trunk provider and they say they see the invite from my system but they receive no response to the challenge sent from their system, they think that Frontier (we were with Verizon Fios, now Frontier) my be blocking port 5060. I have tried changing the port but no matter what port I try it will not pass firewall checker Test2. Does 3CX not allow us to change the port? Inbound calls working fine. Thanks for any suggestions.