I have encounted a error reply with SIP/2.0.501 Not Implemented &SIP/2.0 404 Not Found at the same time. The original VOIP server is connected with ISP well. Once I switched to freepbx and used the original VOIP server as a outbound proxy, it resulted “SIP/2.0.501 Not Implemented &SIP/2.0 404 Not Found”.
All the local phone calls are fine. Is there any setting I should modify it ?
If one of these is a response to OPTIONS, that’s not a problem. FreePBX is just testing that the server is still alive and reachable; any error is an ok response for this purpose.
Find out what request(s) other than OPTIONS are eliciting the 404 and 501.