493 4xx Client error RFC 3261
SIP 493 Undecipherable
The request contained an encrypted S/MIME body the server could not decrypt.
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Common causes
- S/MIME key mismatch (rare in practice).
How to fix it
- Check certificates, or disable S/MIME.
Seeing 493 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.