Lookerstudio can't connect to RDS MySQL

Hello,

When I try to connect RDS MySQL it returns 503 Service Unavailable

{“reason”:23,“errorStatus”:{“reason”:23,“code”:14,“reasonStr”:“JDBC_BACKEND_ERROR”,“errorCategoryStr”:“DATASET_CONFIGURATION”,“category”:5,“uniqueErrorCode”:“15ca76ef”},“params”:{“errorId”:“15ca76ef”}}

I also enabled SSL and added server certificate. Thanks in advance for any help.