What happens when you try to buy the app again? As I said, you cannot buy it twice with the same account. So one of those two things should happen:
- the Store notices that there already is a licence and the Pro version will be automatically activated (but the same should happen when you use the "Restore purchases" button)
- the Store "allows" you to buy the app again and you pay again - in this case, you were logged in with a different App Store account. You will not see the same purchase for the macOS app in the purchase history of a single Apple account: https://support.apple.com/en-us/HT204088/
It would be fantastic if you could let me know which if those two cases happened for you, or if it was something else.
It would help me to figure out what I could improve to prevent such issues in the future. I am always trying to improve the FAQs so that questions & irritations like these don't come up