429 4xx Client error RFC 3892
SIP 429 Provide Referrer Identity
The REFER target requires a valid Referred-By token.
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Common causes
- Transfer security policies.
How to fix it
- Enable Referred-By on transfers.
Seeing 429 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.