SIP
404 Not Found
The user specified in the Request-URI does not exist at the domain. The server has authoritative information that the user does not exist.
When You See This Code
When calling a number or SIP address that does not exist on the server. Different from 480 (user exists but is temporarily unavailable).
How to Fix
Verify the SIP URI or phone number. Check if the user is registered on the correct domain. Ensure the domain is correct.