Stacking rewards
Currently you can only use one coupon at checkout. Using multiple coupons is not permitted. But, you can use a coupon with a gift card at checkout.
Using rewards with discounted products
Sometimes the way that a store discounts an item can affect coupon use. If the checkout rejects your coupon with a sale item, you will need to reach out to the store's customer support and see if they support reward use with discounted items.