The HyperText Transfer Protocol (HTTP) 400 Bad Request response status code indicates that the server cannot or will not process the request due to something that is perceived to be a client error (for example, malformed request syntax, invalid request message framing, or deceptive request routing).
What causes a 400 Bad Request error?
The HTTP error 400 can occur due to incorrectly typed URL, malformed syntax, or a URL that contains illegal characters. This is surprisingly easy to do by mistake and can happen if a URL has been encoding incorrectly.