Which HTTP status Code means that the server cannot or will not process the request...

The HTTP status code 400 indicates that the server cannot or will not process the request due to a client error.

HTTP Status Code 400 - Bad Request:

Meaning: The server cannot process the request due to a client-side error. This could be due to malformed request syntax, invalid request message framing, or deceptive request routing.

Common Causes: Typical reasons for a 400 Bad Request include incorrect URL formatting, invalid query parameters, or unsupported characters in the request.

Client Error Category: Status codes in the 4xx range indicate client errors, where the problem lies with the request sent by the client rather than the server.

Other Status Codes:

100 - Continue: Informational status code indicating that the initial part of a request has been received and the client can continue with the rest of the request.

203 - Non-Authoritative Information: The server successfully processed the request, but the information may come from a different source.

303 - See Other: The server is redirecting the client to a different resource, typically using the GET method.

References:

HTTP Status Codes: MDN Web Docs

RFC 7231: HTTP/1.1 Semantics and Content