437 4xx Client error RFC 8224
SIP 437 Unsupported Credential
The verifier does not support the credential used to sign the Identity header.
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Common causes
- Certificate from an untrusted STI-CA.
How to fix it
- Use a certificate chain trusted by the terminating carrier.
Seeing 437 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.