Consult your network admin/team to determine what is blocking access to the repository.
The following is the protocol/port info that Toad uses to connect:
Connect: TOADCLOUD_USER@(DESCRIPTION= (ADDRESS= (PROTOCOL=TCP)(HOST=toad.ch4y2wqmtnom.us-east-1.rds.amazonaws.com)(PORT=3306))(CONNECT_DATA= (SERVER=SHARED) (SERVICE_NAME=TOAD)))