How to raise an error using CUSTOM.PLL

Hi all,

We have one requirement to raise an error using CUSTOM.PLL upon the choice made by the User on a Standard PO Form.

If User Clicks on Approve button then upon validations,a dialog box has to be displayed with "Yes" and "No" buttons.

If he clicks on No then we have to raise an error and the form navigation should not get into Approval Form.

I have tried using Raise_application_form_trigger but it didn't stop the navigation.