What is a 400 error?

Error 400 Bad Request is an HTTP status code indicating that the server cannot process the client's request due to incorrect syntax or malformed request.

Main causes include:

• Incorrect HTTP request syntax: Errors in the request structure (e.g., invalid characters, omissions in the protocol).
• Invalid characters in URL: Use of characters not allowed in URLs.
• Incorrect request headers: Improperly formed or missing required headers.
• Data type mismatch: Sending data in a format the server does not expect.
• Request headers too large: The server limits the size of headers.

This is a client-side error, not a server error. The server recognized the request as incorrect and refused to process it before attempting to understand its content.