Apple handles all of the billing and tracking of In-App Purchases.
They won’t let you pay twice for the same item.
Therefore, if you’re certain you purchased Pro with the same Apple ID that you’re currently logged in with you can go ahead and use the Get Pro button to restore Pro (see the video below).
- If the buttons on the upgrade page are greyed out you need to close and re-open the app. To do this, double tap the home button and make sure you swipe PolyNome off the screen. Then tap the icon to open it again.
- The Pro Upgrade is a separate thing from buying the App on the App Store. If you haven’t gone through the process of buying Pro before then you don’t already have it.