title: iOS - Inapp purchase - subscriptions
body: <p>I'm having in-app purchase subscriptions in my app. I'm able to integrate and make subscriptions successfully. There are 3 different subscriptions, monthly, quarter and yearly.
  So if user subscribes to monthly user can use that feature for 30 days. There's no server in my case. Only availability of some features will be activated/deactivated according to subscription.
  <br>
  When ever the app starts, i want to check whether user paid for subscription or not. If I'm maintaining some bool value in subscriptions, what if the user has deactivated the subscriptions from settings? How can I detect whether the subscriptions are valid or not?</p>