Message Oracle RMAN-05000 - CONFIGURE AUXNAME required for datafile string

ERRORCONFIGURE AUXNAME required for datafile string
CAUSEEither: -) The control file mounted by the auxiliary database does not have an entry for this datafile, therefore file name conversion is not possible. -) A COPY DATAFILE TO AUXNAME command was issued, but no auxname was set for this datafile.
ACTIONUse the CONFIGURE AUXNAME command to specify a file name that the auxiliary database can use as a restore destination.