Changes to Find one existing candidate by X identity

the response property error became required for the status 400

the response property error became required for the status 401

the response property error became required for the status 403

the response property error became required for the status 404

the response property error became required for the status 409

the response property error became required for the status 429

the response property error became required for the status 500

the response property error became required for the status 503

endpoint added