I'm not sure exactly how I did it. I purchased a game and after installing w10m with a clean install my purchase app was gone (as expected) what I did was open Store beta found the game installed it over. Next I opened store (regular) and found the app and installed that as well. Inside the app (with both stores still opened) I tried to purchase again. And it popped up that I needed to install the key (purchase) and I got a small app to install. All was fine after. Hope this helps in some way