Setting up a new system and extension to extension works fine. Outbound calls work but inbound calls fail. Firewall test passed. Using wireshark, I can see the SIP "invite" from Twilio but 3CX responds with Status-Line: SIP/2.0 407 Proxy Authentication Required. I have read the 3CX - Twilio setup doc - but it appears to be for an earlier version of 3CX... the options listed don't seem to exist in v15. I suspect something the SIP Trunk - Inbound Parameters needs tweaked but have to idea how to debug this issue.