ORA-01274: cannot add datafile 'string' - file could not be created

admin

ORA-01274: cannot add datafile 'string' - file could not be created
Cause: Automated standby file management was disabled, so an added file could
not automatically be created on the standby. The error from the creation attempt is
displayed in another message. The control file file entry for the file is
'UNNAMEDnnnnn'.
Action: Use the ALTER DATABASE CREATE DATAFILE statement to create the
file, or set STANDBY_FILE_MANAGEMENT to AUTO and restart standby
recovery.