Preventing Unlimited Free Trials with Anonymous Users on New Devices

I'm facing a challenge with managing trial offers for anonymous users on new devices
 

The Problem

RevenueCat’s checkTrialOrIntroductoryEligibility is iOS-only, so I’ve built a workaround using allPurchasedProductIdentifiers to determine trial eligibility. It works like this:

const customerInfo = (await Purchases.getCustomerInfo()).customerInfo;

const numPurchases = customerInfo.allPurchasedProductIdentifiers.length;

if (numPurchases > 0) {
  setShowTrialOffer(false);
}

This works as long as the user stays on the same device because RevenueCat caches the Anonymous ID. However, if the user:

1. Starts a free trial
2. Cancels the trial before it ends
3. Deletes and reinstalls the app (or switches devices)

RevenueCat creates a new Anonymous ID when the user reopens the app. As a result, allPurchasedProductIdentifiers will be empty. This allows the user to start another free trial, repeating the process indefinitely.

Potential Solution: syncPurchases

Calling restorePurchases could prevent this, but it may trigger OS-level sign-in prompts, so RevenueCat recommends syncPurchases instead. However, the documentation is unclear:

• General Docs:

  "syncPurchases allows you to programmatically trigger a restore. This method, like restorePurchases, reactivates any content previously purchased from the same store account."

• SDK Docs:

  "syncPurchases sends all purchases to the RevenueCat backend. Call this when using your own subscription implementation anytime a sync is needed, like after a successful purchase."

These descriptions seem contradictory:

• Does syncPurchases pull past purchases from the app stores?
• Or does it just sync purchases from my app to RevenueCat?

Key Questions

If syncPurchases does pull past purchases from the app stores, what happens in this scenario?

1. A user starts a trial (RevenueCat creates AnonymousAppUserID#1)
2. The user deletes and reinstalls the app (RevenueCat creates AnonymousAppUserID#2)
3. The user opens the app, and I call syncPurchases.

After calling syncPurchases:

• Will CustomerInfo.originalAppUserId return AnonymousAppUserID#1?
• Will CustomerInfo.allPurchasedProductIdentifiers include the original trial?
• Will future webhooks for the user have AnonymousAppUserID#1 in the original_app_user_id field?

Any clarity would be greatly appreciated!

Chris