All HTTP status codes

HTTP 421 Misdirected Request

Client Error

The request reached a server that isn't configured to answer for that scheme/authority — common with HTTP/2 connection reuse across hostnames.

Defined in RFC 9110

Common causes

  • HTTP/2 connection coalescing sending a request to the wrong virtual host
  • SNI/SAN certificate covering hosts the backend doesn't actually serve

How to fix it

  1. Retry on a new connection

  2. Align certificates and server routing so coalescable hosts are truly served

Related status codes

400 Bad Request

The server can't or won't process the request because the client sent something malformed — invalid JSON, bad query parameters, broken headers or framing.

404 Not Found

The server can't find anything at the requested URL. It says nothing about whether the resource ever existed or will exist.

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