Problem With Mandatory fields in iw21 Notification

Hello All,

I have a requirement where in i have  to add custom fields in a custom additional tab through CMOD Project.

I have implemented the same.

Now, i have to make certain fields mandatory here. I have implemented a logic to make the screen custom fields in the additional custom tab mandatory by using the following code in PBO section.

IF VIQMEL-ZZFAULT_SOURCE EQ 'TSR' .

  LOOP AT SCREEN.

    IF        SCREEN-NAME = 'QMEL-ZZAUDIT_NUM'.

              SCREEN-REQUIRED = '1'.

              MODIFY SCREEN.

    ENDIF.

  ENDLOOP.

Now , this logic works only when we go to this tab. However if we don't enter this tab and try to save the notification, the custom mandatory fields do not act as mandatory and saves the notification.

Kindly suggest.

I want these fields to act mandatory through out the transaction.