How can users use coupons?

I. Merchants do not check the option for stackable coupons

After users receive coupons, they can select the coupons to use when making payments on the product detail page. Only one coupon can be used for each payment, and users can choose not to use any coupons.     

II. Merchants set stackable coupons

After users receive coupons, they can select the coupons to use when making payments on the product detail page. Multiple stackable coupons can be used for each payment, and users can choose not to use any coupons.