// REFERENCE
511 Network Authentication Required
Class: 5xx
You need to authenticate on the network to get access (the classic hotel/airport WiFi captive portal). It's issued by the network, not the destination site.
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500
500 Internal Server Error 501
501 Not Implemented 502
502 Bad Gateway 503
503 Service Unavailable 504
504 Gateway Timeout 505
505 HTTP Version Not Supported
500 Internal Server Error 501
501 Not Implemented 502
502 Bad Gateway 503
503 Service Unavailable 504
504 Gateway Timeout 505
505 HTTP Version Not Supported
Semantics per RFC 9110 and the IANA status code registry. Educational content.