What's the point of this API? When I click the link its behavior is undocumented. It seems an actual solution to OP's question can be found here: https://stackoverflow.com/a/78658285/220287

When I try this and take the device out of airplane mode, I find Xcode loses connectivity to the device and I'm back to square one. Not sure if that's 100% of the time or just intermittent. This issue is a complete PITA.

The scenario in which I'm seeing appAccountToken go missing is when you resubscribe from Settings>App Store>Sandbox Account>Manage rather than from the app itself. I'm not clear why the (cancelled + expired) Subscription even keeps showing up there at all. Is this even possible in Production? (Also, "Clear Purchase History" on the sandbox testing account doesn't remove the cancelled + expired sub from this page - at least not yet, in my testing.)

@krystian_laubach "does it mean that original_transaction_id is globally unique and we can use it to identify user?". I don't think so - the same user may have several IAPs (depending on your product structure), and a resubscribe >180 days would apparently generate a new INITIAL_BUY (per @oscaretu's comments above). appAccountToken may be what you need (if you're able to use StoreKit 2). Interesting that you see notifications coming quickly from Apple - so far in the sandbox, I've found them to be very laggy (several minutes after purchase), which means you can't really rely on them to entitle the user's account server side in a timely fashion.

@nbe I think appAccountToken handles this use case - it's a UUID you can pass in at the time of purchase into StoreKit2, which is then included with each v2 App Store Server Notification you receive. It's intended to address exactly the problem of correlating purchases with user accounts. See https://developer.apple.com/videos/play/wwdc2021/10114/

@oscaretu - very useful, thank you. I'd love to know if the 180 days behaviour is documented somewhere also. Can't find any other reference to this online (although it makes sense, as it seems 180 days is the max time to refund a credit card payment, per other search results I'm seeing for other payment processors).