There might be a few reasons:
1. The coupon is no longer valid. To find out, go to My Coupons. 
If the coupon status says Expired or Used, this means that you can’t use the coupon anymore.
2. The products are not all from the same store.
Seller coupons can only be used on items of the same seller. Please check if the coupon can be used on all items in the store. You can click VISIT STORE NOW to start shopping.
Note: Some seller coupons can only be used on a selection of products.
3. You’re not meeting the minimum spending requirements.
For example, if a coupon is only valid for orders over US $100, but your order value is $80, you can’t use the coupon.
