不续订订阅：转回时间

I'm creating an app that will unlock features to users for a limited time. Premium features let's call them. They can buy a subscription for a month, 6 months or a year. These subscriptions would be non-renewing. After a lot of searching the web and finding very different "solutions", I turn to StackOverflow for what the best should be.I'm creating an app that will unlock features t