You expected a 200 code, but received 400 (bad request). What will you do? The request is fully valid and complies with the contract, but the error still occurs.

If the request is valid and matches the contract, but the server returns a 400 Bad Request, you should:

• Verify that the request indeed complies with the API specification (e.g., correct headers, body format, data types).
• Check the server logs or error response — often, they contain details on why the request was rejected.
• Ensure there are no encoding issues or hidden characters in the request.
• Check if the contract or server logic has changed (e.g., new required fields).
• Try reproducing the request using different tools (Postman, curl) to rule out client errors.
• If possible, contact the server developers for clarification.

Thus, even if the request seems valid, the error may be caused by validation nuances on the server, mismatched expectations, or a bug.