HTTP 400 Bad Request means the server cannot process the request because the client sent something invalid — malformed syntax, invalid request framing, or deceptive routing. The client should not repeat the request without modifications.
The request contains invalid JSON, XML, or form data that the server cannot parse.
Required query parameters are missing, have wrong types, or contain invalid characters.
The URL, headers, or body exceed the server's configured maximum size.
Verify the request body is well-formed JSON/XML and all required parameters are present.
curl -v -X POST -H 'Content-Type: application/json' -d '{"key":"value"}' https://api.example.com/endpointMany APIs return a detailed error message in the 400 response body explaining what was wrong.
Compare your request against the API documentation to ensure all required fields, headers, and formats are correct.
Ensure special characters in query parameters are properly URL-encoded.