Dataguard Manager User for Container db (c##dgmgr) Fails (24354703)

Problem Summary: When creating a data guard protection group with the dataguard manager user set to sysdba_username=c##dgmgr, the operation fails with the following message:

Unable to connect using connect string "c##dgmgr/<password>@<instance>". 
Check that the password or connect string is correct and that the database instance is running

Workaround:To solve this issue, set sysdba_username=sys.