I can access it OK from the web store but I like how the itch app keeps them all up to date. What's up with it not showing up under purchases?
Let Nature Flow from your Brush · By
You may want to check that the purchase is attached to your account. If you bought it while logged out then you'll be prompted to log in on the download page generated, and that will attach it to your account. Otherwise, it will show your account name on the purchase page when it's connected. A purchase must be connected to an account in order to be accessed from the app. Hope that helps.