SIP error codes
SIP errors are status reports for internet-based phone calls. Much like a web browser shows a "404 Not Found" message when a page is missing, your phone system uses three-digit codes to explain why a call did not go through.
As a general guide:
Errors starting with 4 usually indicate a problem on the user's end, such as a wrong password or a mistyped phone number.
Errors starting with 5 or 6 typically indicate a problem with the service provider's equipment, or that the person you are calling is unavailable.
These codes help you identify whether you need to fix your settings, check your internet connection, or wait for a server to come back online.
