I am developing an app which will be free to download from the Apple App store. However, users will be able to subscribe for advanced features which include the use of a web service. I would like the ability to detect those users who have subscribed and then cancelled their subscriptions so I can halt the use of the web service. I would like to do this automatically.
I know PayPal is one way to set up subscriptions, but is it able to detect when people cancel their subscriptions and notify me in a way that my web service can be automatically updated?
Any other advice or pointers welcomed - I cant be the first person/company looking to do this. But I dont really know where to start!