There are some reasons for this, one of which is that only one coupon code can be used per order, so check to see if a discount has already been automatically applied to your order. If so, you won’t be able to add another discount to this order. And also please check to make sure your promo code isn’t expired, case-sensitive or unavailable for the items in your cart. Or the Stellar Data Recovery promo code you applied can only be used for some items or some categories which the items in your cart are not qualified for this discount.