For non-AppStore apps like Lunar, I use the macOS SDK from Paddle.com. It provides trials, license activation UI, payments and checkout UI, both in-app and on web. Here's how I use it: https://github.com/FuzzyIdeas/Lowtech/blob/main/Sources/Lowt...

For App Store apps I have my own custom solution which uses https://github.com/IdeasOnCanvas/AppReceiptValidator to see if the app has been bought, and if it isn't, I have a time and usage based expiry logic. When the timer expires, I block key functionalities of the app and show this screen: https://shots.panaitiu.com/o6qnP8