Restores any managed purchases made on this platform. For example if a user purchased at item then reinstalled the app the app would return 0 for GetInAppPurchaseAvailable unless it was purchased again or restored using this command.
Even though purchasing again wouldn't charge the user again for non-consumable items, using this restore command is a better user experience. Apple require you to have a button that calls this function somewhere in your app.
After calling this command you can call GetInAppPurchaseAvailable2 to check for purchases, it may take some time for the purchase state to update, so check GetInAppPurchaseAvailable2 regularly. This command is supported by both iOS and Android
InAppPurchaseRestore()