App store says I have an app purchased but won

So I recently stopped using family sharing cause it wasn’t necessary for me to keep having that. But, I would have/use an app that my parent had purchased. After we stopped using family sharing, I went to check what would happen at the app I was using, it told me I had to buy it. And so I try to go and buy it but the App Store says it’s already purchased. Although it says it’s already purchased, it won’t let me download it. So, I can’t buy it or download it again. Why is this?