412 Precondition Failed
Meaning
One or more conditions given in the request header fields evaluated to false. The server does not meet a precondition specified by the client.
When to Use
When the request includes conditional headers (like If-Match, If-Unmodified-Since, etc.) and the server determines that one of those conditions is not met for the target resource.
Example
A GET request with If-Unmodified-Since on a resource that has been modified since that date returns 412 Precondition Failed, because the precondition was not satisfied.
When Not to Use
Do not use if there were no precondition headers in the request. If the request fails for other reasons unrelated to conditions (e.g., validation), use a different status code.
Source
RFC 9110