I have done some searching on this topic, but I haven’t found anywhere that addresses it directly.
I have an iOS app with a renewing annual subscription. If I wanted to offer existing subscribers an incentive to share the app, such as giving them an addition month of service for every relevant action. I don’t see a way to do this without disrupting their existing subscription, even if I took care of the accounting of starting the one-month of free access and then tried to trigger their next month.
The best I could think of was to offer them to renew with a different annual subscription that had a 1 month free trial. But that doesn’t necessarily scale well for different numbers of incentives.
I hope that makes sense.