How can I re-download my purchase from the Mac App Store without having to pay again?

macOS 10.13 High Sierra: All purchases from the Mac App Store are stored in the “Purchases” tab on top of the Mac App Store. If you should need to re-install your purchase or install it on another Mac, simply navigate to that pane. Important note: You have to be logged in with the same Apple App Store / iTunes account you used for purchasing the app.

macOS 10.14 Mojave or later: Please click onto your profile after you signed in to get an overview of your purchased applications.