onPurchaseSuccess fires on subscription renewal in sandbox mode

[mattwoodage]

Can someone please confirm this is expected and desired behaviour because i can't find it in the documentation.
I'm on version 3.1.8

I am testing subscriptions in sandbox mode on IOS
I make a purchase and onPurchaseSuccess is called correctly and I call finishTransaction and everything is good

If i leave the app closed for a few hours, in this time the sandbox subscription expires and renews multiple times. I have mine set to a 3 month subscription and set to 3 minute renewals in the developer account so it expires after 9 minutes)

When i then open the app, onPurchaseSuccess is called for each of these new subscriptions. They are each new transactions with unique transaction ids. This is recorded in my database.

I can see in the documentation that onPurchaseSuccess will re-fire if the transaction was not completed. But should it be behaving as i've described here? Can i rely on this in production (obviously at a monthly interval)?

[hyochan]

Yes — what you’re seeing in iOS sandbox is expected. Each auto-renewal creates a new transaction with its own transactionId, and when you reopen the app the store delivers those purchase updates, so onPurchaseSuccess will fire once per renewal. In production you’ll see the same pattern, just at real billing intervals (e.g., monthly), not every 9 minutes.

How to handle it safely

• Finish every renewal: call finishTransaction after you validate/grant.
• Make it idempotent: persist processed IDs (iOS: transactionId / originalTransactionId) and no-op if already handled.
• Don’t rely only on client callbacks: on app launch, validate the receipt on your server to derive entitlements. Consider App Store Server Notifications v2 for reliable server-side renewal events.
• Note on docs wording: our docs say the callback re-fires for unfinished transactions; in sandbox, renewals themselves are new finished-required transactions, so you’ll naturally see multiple firings after time passes.

[mattwoodage]

Thank you @hyochan. Now i have managed to get the server notifications in place the onPurchaseSuccess is less critical and just confirms what i've already stored in my database. I didn't find the apple documentation too helpful. Yours is much better.