Message Oracle ORA-38799 - Cannot drop guaranteed restore point internally created for snapshot standby

ERRORCannot drop guaranteed restore point internally created for snapshot standby
CAUSEAn attempt is made to drop the guaranteed restore point Oracle created internally for a snapshot standby.
ACTIONUse the alter database convert to physical standby command to convert the snapshot standby to a normal physical standby. This will automatically flashback the database and drop this guaranteed restore point.