Question about setting up a promotion


I am trying to set up a promotion where if a customer selects any three items from category A, B or C they get a discount.


Group : if all these conditions are true

Categories A, B and C

Total Products in cart: equal or greater 3


X off the price

What happen is if there are 3 items in the cart, the discount is applied regardless of the categories so if items are in the cart from category A, B and T are in the cart the discount is still applied.

Could someone tell me if what I want to do is possible and where I’ve gone wrong?