Just bought AoE: Definitive edition, can't actually download it from anywhere?

Maybe I'm just stupid, but I bought the game, and I can't find where I'm supposed to download it!

I logged in to my Microsoft account, went to my order history, and click "Install", and all it does is show me a product key. Where am I supposed to put the product key? How do I actually install it? I can't figure this out. I even went to the game page while logged in, and it just says "buy for 19.99!" What in the world is going on with microsoft right now?