Background
You were refunded for the app, but have changed your mind and want to repurchase it. However, attempting to do that might give the following message:
Solution
It's likely an App Store bug. Please do the following:
1. Open the Settings app > Apple ID > Media & Purchases > Sign Out.
2. Visit GoodNotes App Store page and choose Get.
3. Sign in to your Apple ID account and continue with the purchase process.