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HTTP Status Codes

HTTP 510 Not Extended

510 Not Extended

The server requires further extensions to the request before it can fulfill it; this code is now marked obsoleted in the registry.

510 Not Extendedgeneral

Observed message

510 Not Extended

Why it happens

  • The server expects an extension or additional request semantics that were not provided.
  • Legacy or experimental HTTP extension behavior is involved in the request path.
  • A historical implementation still emits this code even though the registry now marks it obsoleted.

How to fix it

  1. Check whether the server expects an extension-specific request format or negotiation step.
  2. Review the server or intermediary implementation that is still emitting 510 responses.
  3. Prefer modern, currently supported protocol behavior if the implementation can be updated.

Official reference

IANA: HTTP Status Code Registry

Related errors

100 ContinueHTTP 100 Continue101 Switching ProtocolsHTTP 101 Switching Protocols102 ProcessingHTTP 102 Processing103 Early HintsHTTP 103 Early Hints

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510 Not Extended: what it means and how to fix it | Error Atlas