407 4xx Client error RFC 3261
SIP 407 Proxy Authentication Required
Like 401, but the client must authenticate with the proxy. Carriers commonly challenge outbound INVITEs this way.
Typical Q.850 / ISDN cause: 21 (Call rejected)
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Common causes
- Normal digest challenge on outbound calls.
- Missing or wrong trunk credentials (looping 407s).
How to fix it
- One 407 followed by a re-sent INVITE with Proxy-Authorization is normal.
- If calls fail at 407, set the trunk username and secret, and confirm the PBX is set to respond to challenges (for example, outbound auth in PJSIP).
Seeing 407 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.