Trigger Global Function during New Item Request (NIR)

Summary:

I am trying to trigger a Global Function at the end of an NIR; as soon as the NIR is approved the Global Function should be triggered.

I have tried to use a Product Ruls like this one (Type: Validation, Association Type: Item class):

IF ([Item].[Item Basic].[Approval Status] == "Approved"

Validation Condition: InvokeGlobalFunction("XYZ", [Item].[Item Basic].[Item])

or even an IF condition like

changed([Item].[Item Basic].[Approval Status])

But these rules aren't firing, i.e. the Global Function isn't triggered.

I have also tried to trigger directly in the Application Composer using Server Scripts in the Standard Objects but there is no Standard Object for NIRs.