Helge Heß published an Open Source component to use the modern FastSpring web API so you can display a sheet to purchase a license of your app within your app.
It’s not yet a native in-app purchase UI or anything, but you can
- display your product from your FastSpring store,
- process orders in the sheet, since it’s just a
- automatically activate the app after the order is completed.
The last part is probably the most important to me. It’s what I like most about the
FSCheckoutSheet on GitHub: https://github.com/ZeeZide/FSCheckoutSheet/