Rejecting sales Order item, if the corresponding PO Item is deleted

Dear Friends,

I have requirement to set reason for rejection in the sales order item if the corresponding purchase order item is set to deleted.

I have applied the logic in user-exit MV45AFZZ, it's not working while deleting line item of PO.

but it's getting triggered when we change the PO line item quantity and the same is reflected in sales Order Item.

can you please help me on this by providing the right user-exit.

Thanks,

Munvar Basha.