412 Precondition Failed
A precondition in the request headers, such as If-Match or If-Unmodified-Since, evaluated to false, so the server did not apply the request.
4xx · Client error
Typical causes
Optimistic concurrency: the resource changed since the client read its ETag, so an update based on the old version is refused instead of overwriting it.
Defined in RFC 9110, §15.5.13