PL/SQL FUNCTION arguments with IN/OUT declaration fails

CREATE FUNCTION get_bal(acc_no IN NUMBER) 

   RETURN NUMBER 

   IS acc_bal NUMBER(11,2);

   BEGIN 

      SELECT order_total 

      INTO acc_bal 

      FROM orders 

      WHERE customer_id = acc_no; 

      RETURN(acc_bal); 

    END;

/

You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'IN NUMBER)

CREATE FUNCTION get_bal(acc_no NUMBER) 

   RETURN NUMBER 

   IS acc_bal NUMBER(11,2);

   BEGIN 

      SELECT order_total 

      INTO acc_bal 

      FROM orders 

      WHERE customer_id = acc_no; 

      RETURN(acc_bal); 

    END;

/