In-App Purchases are handled in the same secured way like AppStore purchases.
For payment, just like on the AppStore, you just need to enter your Apple ID password (or Fingerprint – if enabled) and the displayed amount will be paid using your Apple account.
My App doesn’t use subscriptions or recurring payments and you only have to pay once to use the selected feature forever – you basically own it.
Even if you have multiple devices, you just have to pay once.
If you lost or sold your device where you purchased a feature via In-App Purchase, don’t worry. You can always use the “Restore” button to restore any previous purchase – you don’t have to pay twice.
PLEASE NOTE: If the “Restore” button is not working, it might be the case that your purchase has not been synchronized to your device for some reason. But don’t worry. Instead, just hit the “Buy” button. You may need to enter your Apple ID or fingerprint and then you should see a message saying that you already purchased this item and if you want to download that item for free again.