Hi,
Sometimes You can get “RMAN-06758: DB_UNIQUE_NAME is not unique in the recovery catalog ” error.
Details of error are as follows.
RMAN-06758: DB_UNIQUE_NAME is not unique in the recovery catalog
Cause: RMAN could not identify which SPFILE to restore for this target database, because the recovery
catalog contained two or more different instances of this database, each with different DB_UNIQUE_NAME values.
Action: Use the FOR DB_UNIQUE_NAME option to specify the name of the instance whose parameter file you want to restore.
This error is related with the db_unique_Name, to solve this error add db_unique_name into restore script as follows.
RMAN> restore spfile for db_unique_name MSDB;
Do you want to learn more details about RMAN, then read the following articles.
https://ittutorial.org/rman-backup-restore-and-recovery-tutorials-for-beginners-in-the-oracle-database/