SIP Error Codes

Think of SIP errors as the "status reports" for internet-based phone calls. Much like a web browser gives you a "404 Not Found" message when a page is missing, your phone system uses these three-digit codes to explain why a call didn't go through.

Errors starting with 4 usually mean there’s a mistake on the user's end, like a wrong password or a mistyped phone number. Errors starting with 5 or 6 typically mean the problem is with the service provider’s equipment or that the person you're calling is simply unavailable everywhere. Essentially, these codes act as a diagnostic shorthand to help you figure out if you need to fix your settings, check your internet connection, or just wait for the server to come back online.