PLS-00103: encountered the symbol "ADD" when expecting one of the following: in like like2 like4 likec between member submultiset

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trigger

CREATE OR REPLACE TRIGGER MOA_patcharges_balance
BEFORE INSERT ON patcharges
FOR EACH ROW
DECLARE
v_outstanding number;
both_null EXCEPTION;
both_not_null EXCEPTION;
BEGIN
SELECT Moa_patcharges.outstanding INTO v_outstanding
FROM Moa_patcharges
WHERE Moa_patcharges.patID= :new.patID AND
entryDate = (SELECT MAX(entryDate) FROM Moa_patcharges
WHERE Moa_patcharges.patID= :new.patID);
IF (:new.payments IS NOT NULL AND :new.charges IS NOT NULL)
THEN RAISE both_not_null;
END IF;
IF (:new.payments IS NULL AND :new.charges IS NULL)
THEN RAISE both_null;
END IF;
IF (:new.charges IS NOT NULL AND :new.payments IS NULL)
THEN RAISE charge_not_null;
END IF;
IF (:new.payments IS NOT NULL AND :new.charges IS NULL)
THEN RAISE payments_not_null;
END IF;
EXCEPTION
WHEN charges_not_null THEN
:new.outstanding := v_outstanding + :new.charges;
dbms_output.put_line ('This is the new balance' || TO_CHAR(:new.outstanding));
WHEN payments_not_null THEN
:new.outstanding := v_outstanding - :new.payments;
dbms_output.put_line('This is the new balance' || TO_CHAR(:new.outstanding));
WHEN both_null THEN
RAISE_APPLICATION_ERROR (-20325, May not add a record with both payment and charge information.');
WHEN both null THEN
RAISE_APPLICATION_ERROR (-20325, 'May not add a record with both payment and charge information.');
END;
/

What I have tried:

EXCEPTION
WHEN charges_not_null THEN
:new.outstanding := v_outstanding + :new.charges;
dbms_output.put_line ('This is the new balance' || TO_CHAR(:new.outstanding));
WHEN payments_not_null THEN
:new.outstanding := v_outstanding - :new.payments;
dbms_output.put_line('This is the new balance' || TO_CHAR(:new.outstanding));
WHEN both_null THEN