Hi,
Coupons apply to the whole order not to individual products.
If you turn on the "Coupon percentage applies to product only" option of the coupon, you can make it so that the value of the coupon in only calculated on a subset of the products in the cart with a percentage coupon, but for a fixed value, it doesn't change anything. When you add the coupon to the cart, the fixed value is added to the cart, not to individual products. And you can't dynamically change the fixed value with the options available.
I see these potential solutions:
1- You use a percentage instead of a fixed value for your coupon.
2- You contact AWO Coupon Pro to see if their coupon system for HikaShop can support that.
3- You develop a HikaShop plugin to override the coupon system calculations. I would personally recommend to implement the trigger onBeforeCouponCheck in that case to set the coupon value based on your rules. You can read more about that trigger on our developer documentation page.