ORA-16930
Cause
Either an open was initiated for this standby pluggable database at one of the instances and was not yet open when redo apply services was starting, or this standby pluggable database was previously open in Real Time Query mode and redo apply services is waiting for this standby pluggable database to be open. Data Guard broker will start redo apply services when an instance of this standby pluggable database is open and available to enable Real Time Query.
Action
If the standby pluggable database is in the process of opening, no action is necessary. Data Guard broker will start redo apply services once it is opened. If not, consider opening the standby pluggable database at one of the instances, or issue the DGMGRL command EDIT PLUGGABLE DATABASE name SET STATE=APPLY-ON to start recovery at a mounted instance in non-Real Time Query mode.