Create new product attribute on modifier

Hi All,

I have a scenario, when a customer order items from a certain group item (let's say Group Item A Contain Item A1, Item A2, and Item A3), with minimum order 80 pcs, they will get Item A4 10 pcs for free. The condition only read minimum quantity order, without seeing the item combination (the customer may order Item A1 80 pcs, or order Item A1 20 pcs, Item A2 60 pcs, still get the A4 10 pcs for free). I try to create new item category for the items, and create a new product attribute on modifier, but I'm facing