Successful in-app purchases can be restored free of charge using the button in the top right of the purchase screen in myPWS. It is imperative that the current device is connected to the same Apple ID that was used to purchase the in-app products, otherwise the purchases cannot be restored.

If, for some reason, restoring an In-App purchase fails, you can also initiate a new purchase. However: make sure you do that under the same Apple ID as you did for the original purchase. You then won't be charged twice because the App Store will recognize your purchase from the past!