Integration Server always writes server errors that occur during execution of REST resources in the Administrator API to the error log. A server error is one that results in an HTTP status code in the 500s. However, client errors, those that result in an HTTP status code in the 400s, are not written to the error log by default. If you want these errors to be written to the error log, set watt.adminapi.log.clientErrors true. Changes to this property take effect immediately.