How do I, well, use this coupon?

[Nick]

Game is on sale, coupon can't be used with a sale, and, there's no way to overrule the sale for the coupon:-
https://i.imgur.com/fry5rrl.png

Clicking the "Add coupon" just shows this:-
https://i.imgur.com/tnjE712.png

Which, is basically stating I can't use the discount with the sale, but, I can't disable the sale.