406 4xx Client error RFC 3261
SIP 406 Not Acceptable
The resource can only produce content that the Accept header in the request does not allow.
Typical Q.850 / ISDN cause: 79 (Service or option not implemented)
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Common causes
- Content type negotiation mismatch, rare in voice calls.
How to fix it
- Check the Accept headers sent by the client.
Seeing 406 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.