Oracle Message ORA-16621 - database name for ADD DATABASE must be unique

ERRORdatabase name for ADD DATABASE must be unique
CAUSEAn attempt was made to add a database to the broker configuration that already included a database with the specified name. The database names must be unique.
ACTIONVerify that a unique name is specified for the new database to be added. Also, the database name must match the DB_UNIQUE_NAME initialization parameter of the database.