// REFERENCE
426 Upgrade Required
Class: 4xx
The server requires switching protocols to serve the request (e.g. moving to TLS or a higher HTTP version). It carries the Upgrade header.
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400
400 Bad Request 401
401 Unauthorized (not authenticated) 403
403 Forbidden (access denied) 404
404 Not Found 405
405 Method Not Allowed 406
406 Not Acceptable
400 Bad Request 401
401 Unauthorized (not authenticated) 403
403 Forbidden (access denied) 404
404 Not Found 405
405 Method Not Allowed 406
406 Not Acceptable
Semantics per RFC 9110 and the IANA status code registry. Educational content.