404 4xx Client error RFC 3261
SIP 404 Not Found
The server has definitive information that the user does not exist in the domain in the Request-URI.
Typical Q.850 / ISDN cause: 1 (Unallocated (unassigned) number)
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Common causes
- The dialled number or extension does not exist.
- Wrong number format (missing country code or leading zero).
- No matching route in the dialplan or routing table.
- The extension is not registered and the server returns 404 instead of 480.
How to fix it
- Check the number format the carrier expects (for example +27..., 0027... or 0...).
- Check inbound routes (DID) and outbound route patterns on your PBX.
- Verify the Request-URI domain matches what the server considers local.
Seeing 404 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.