SIP/2.0 404 Not Found

Sent from the proxy when either the intended party does not exist (wrong number dialed) or the user is not registered on that proxy. This message might be sent from the gateway if it's caused by dialing a wrong number.

This is also sent from the proxy in response to INVITE request if device is not registered to that proxy. You can tell if this is the case because the proxy does not authenticate the Invite request with a "407 Authentication Required".

Solutions

1. Make sure proxy/PBX has such number you are sending him
2. Make sure you send number in expected format (configured properly as your Provider expects)
3. Make sure you are registered to the proxy if it is necessary to do so (ask your Provider)