ORA-1651: unable to extend save undo segment by %s in tablespace %s

ORA-1651: unable to extend save undo segment by %s in tablespace %s
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Cause: Failed to allocate an extent of the required number of blocks for saving undo entries for the indicated offline tablespace.
Action: Check the storage parameters for the SYSTEM tablespace. The tablespace needs to be brought back online so the undo can be applied.