400 Bad Request
4xx Client Error

The 400 (Bad Request) status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

RFC 7231 6.5.1


This is a very common server response. It’s the basic “you screwed up” error message to the client.