Unlike with digital products, retail coupons typically have a finite number available for customers to purchase. This number, the coupon inventory, is defined by the number of coupon codes in the code file (for unique coupons) or by the number you enter in the Quantity field (for universal coupons). Service Design Center tracks how many coupons are available for customers to purchase at any specific time, which is the total number of coupons minus the number that have been sold. Once the number available drops to 0 (zero), no more of that retail coupon can be sold (unless it is a universal coupon and you increase the coupon inventory).
The number of available coupons for any retail coupon product is the number in the Available column next to the retail coupon product name.