The request is HTTP PATCH (RFC 5789), application/x-www-form-urlencoded or multipart/form-data (RFC7578) and holds the updated details of the candidate. This is a partial update call, which does not update every detail every time, only the modified ones. The available data fields are listed in Appendix 4.2. If the operation was successful, the response message is HTTP 200 OK. If the request but the data was unchanged, the response message is HTTP 304 Unchanged. If the request cannot be processed due to misformatted or untranslatable data, the API should response with HTTP 400 Bad Request error. If the candidate_ref is not valid then the API should response with HTTP 404 Not Found error. If the request cannot be processed due to data validation errors, the API should respond with HTTP 403 Forbidden and an appropriate error response. (See section 3.6 Error responses).