What to do if the API returns 200 OK, but the response body does not match the contract?

If the API returns a status 200 OK, but the response body does not conform to the contract, the following steps should be taken:

1. Document the discrepancy: record exactly what does not match the contract (structure, data types, required fields, etc.).
2. Notify the API developers: communicate the issue, include examples of responses and expectations.
3. Automate contract validation: use contract testing tools (e.g., Pact, Postman tests) to detect such errors early.
4. Temporarily handle deviations on the client side: if possible, add validation and error handling to prevent failures.
5. Review the contract: it may be outdated or need clarification.

Example of response validation against the contract in a JavaScript test using Jest:

expect(response.status).toBe(200);
expect(response.body).toHaveProperty('userId');
expect(typeof response.body.userId).toBe('number');
// Additional structure and type checks

Thus, it is important not only to check the status but also to validate the response content according to the contract.