in-app purchase, multiple auto-renewing subscriptions having different durations

Question

A question regarding in-app purchase auto-renewing subscriptions:

I'm unclear how to handle the case where a user purchases multiple subscriptions of differing durations. It seems that Apple will recognize if the user has already purchased a given SKU (based on product-id) and prevent re-purchasing (my app gets a failed-transaction event in this case), but if I offer the same content using different product-ids having different durations, then the user can potentially purchase twice or more.

Even if I hide the additional purchase options once the user has subscribed once, they could potentially buy another subscription on an alternate device, and that purchase would/could ultimately be restored to the other device already having a subscription.

Am I supposed to track purchased subscriptions by transaction-ID and product-ID, and calculate an ultimate expiration date? That seems complicated.

Answer 1

Before I proceed, please see the comments on this linked post on why it may be a bad idea to use auto-renewing subscriptions.

Stop me if you've heard this before.
When you choose Auto-Renewable Subscriptions in iTunes Connect, you are given the opportunity to add multiple durations, with different Product ID's to one subscription Family. Apple won't allow a user to purchase multiple, overlapping subscription durations within one family. (If you're using multiple families in your app, please explain the reasoning, so I can give you guidance based on that).

In fact, Apple won't let the user stack different durations of a subscription within one family.

Here's an example.
I (as a user) download the hypothetical Acme app and subscribe with a 1-month subscription. If I do nothing, my subscription will automatically renew at the end of the period with another 1-month subscription. And so on.

But instead I go back in and purchase a 6-month subscription. Apple will tell me (with an alert) that my 6-month subscription will begin at the completion of my current 1-month subscription, and would I like to proceed. If I say yes, Apple will make note of it, but they won't charge me until my current 1-month is up.

Now if I go back in again and purchase a 1-year subscription, then again Apple would respond with an alert telling me that it will begin at the end of my current 1-month subscription. It won't get added to the upcoming 6-month subscription. It will replace it.

In Summary
So a user can only have one Current subscription and one Upcoming subscription (within a family. This is why you use a Family of product durations within a subscription. If you create multiple subscription families then they can exist simultaneously, and you loose that protection.

If, as a developer, you'd like to manually extend, shorten, cancel or stack subscriptions, you should be doing it with Non-Renewing Subscriptions. And if you read the link I posted at the top, you'll realize that Apple may force you to do that.