480 4xx Client error RFC 3261
SIP 480 Temporarily Unavailable
The callee was reached but is currently unavailable: not registered, do not disturb, or not answering.
Typical Q.850 / ISDN cause: 18 (No user responding)
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Common causes
- The extension or softphone is not registered (offline, closed app, lost Wi-Fi).
- Do-not-disturb is enabled.
- Mobile network can't reach the subscriber.
- A PBX returns 480 when no endpoint answers or all are offline.
How to fix it
- Check registration status on the PBX (for example, pjsip show contacts in Asterisk).
- Check the device for DND or wrong registration server.
- For mobile apps, enable push notifications so the app can be woken for calls.
Seeing 480 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 4xx responses
The request has a problem or cannot be completed at this server, usually because of something on the requesting side or the target user.