Coupons can be used for just one service. For example, if the user buys 10 proxies, 10 shared proxies, 10 socks and 10 shared socks and he uses a coupon which can be applied on all services, he will be asked to choose the service on which he wants the coupon discount. If the coupon can be applied just on service proxy, it will be applied automatically just on that service, for the rest of the services he will pay full price.