400 status code means code example

Example 1: 400 http

400 Bad Request 

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
(e.g., malformed request syntax, invalid request message framing, or deceptive request routing).

Example 2: 200 error code

The HTTP 200 OK success status response code indicates that the request has succeeded. A 200 response is cacheable by default. The meaning of a success depends on the HTTP request method: GET : The resource has been fetched and is transmitted in the message body.

from developer.mozilla.org

Example 3: what is error code 400

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 (e.g., malformed request syntax, invalid request message framing, or deceptive request routing).