400 Bad Request is a HTTP status code that indicates the client’s request to the server is invalid or malformed, meaning the server cannot understand or process the request.

This could occur due to a typo in a URL, if the request contains invalid fields or duplicate parameters, or the body does not parse.

400 responses are the result of invalid requests sent by the client and prevent the server from identifying what is being asked.

Sending a 400 status code allows servers to request that the client fix the error before resending rather than erroneously going forward with an unintended behavior.