how to run DBMS_RULE_ADM
You need to use EXEC[UTE] or BEGIN ... END ;.

EXEC DBMS_RULE_ADM.GRANT_SYSTEM_PRIVILEGE(DBMS_RULE_ADM.CREATE_RULE_OBJ, '');


Or:

BEGIN
  DBMS_RULE_ADM.GRANT_SYSTEM_PRIVILEGE(DBMS_RULE_ADM.CREATE_RULE_OBJ, '');
END;
/