Success and Error message for process in processing

We have a process that runs when a page is submitted and we have defined messages for 'Success Message' as 'Processing successful' as well as 'Error Message' as 'Processing Failed'.

A PL/SQL code is run in this process and pseudo code is something like below.

DECLARE
    V_NUMBER   VARCHAR2(250);
    V_REQ  NUMBER;
BEGIN
SELECT REQ_NO INTO V_REQ FROM ZZZ_TBL WHERE ROWNUM=1;
IF :P24_VALID_1 = 'Valid ' THEN    
    UPDATE XXX_TBL
        SET
            M_NUMBER =:P24_MRI,
    WHERE REQ =V_REQ  ;
        COMMIT;
ELSIF :P24_VALID_1 ='Invalid' and :P24_VALID_2 = 'Valid ' THEN
    UPDATE XXX_TBL
        SET
            M_NUMBER ='MRI-'||:P24_NEW_MRI,
    WHERE REQ =V_REQ;
        COMMIT;
END IF;
EXCEPTION
    WHEN OTHERS THEN
       RAISE_APPLICATION_ERROR(-20001,'Something went wrong. NIC Request could not be processed');
END;