Right now, only new signups can apply a coupon. We want to do a "Refer a Friend" discount where the user gets 25% off and the friend gets 25% off. First, we need the ability to let current customers apply a coupon for their next subscription period. Second, we need to be able to restrict coupons so that a user can only use it once (WooCommerce offers this feature). Finally, there needs to be a way to set parameters for a coupon and have unique codes generated for each customer that we can use in an email, like a MailChimp automation. None of these features are available and it is very limiting.