Hey @Matteo Gobbi!
You’ll want to be sure you check if a user ID is already subscribed before allowing a paywall to be displayed, but ultimately, there’s nothing preventing a user from subscribing on two different platforms. The SDK won’t prevent users from making a purchase (even if they already have an active entitlement), so you’ll need to implement this logic on your end.
You’ll need to use custom user identifiers and have the user first log in - and if you’re using our entitlements system, you can check if an entitlement is active or not before showing your paywall on either platform: https://docs.revenuecat.com/docs/purchaserinfo