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What are the best practices for transitioning from a single purchase model to a subscription model on the Microsoft Store?
You could create and publish a subscription add-on first. After the subscription is available, you could move on and submit a new package submission to the Store. Make sure you've implemented all the features in your app and don't forget to set the price to free in the new submission. After that, you could publish the new submission and that's all.
How can I ensure a smooth transition for my existing users? I want to migrate them over to lifetime licenses as part of this change. Are there any technical considerations or challenges I should be aware of when implementing this change in a WinUI3 Windows SDK C# application?
First of all. there is no direct store API could check when user has purchased your app. After you've changed your app as free,
license.IsActive will always be true when you trying to verify the license. This is the key point, you need to check when user has purchased the app by yourself so you could decide whether to directly unlock all feature to them without purchasing the subscription again. You could refer to Gil 1's answer here: https://learn.microsoft.com/en-us/answers/questions/557066/in-case-i-changed-my-app-from-paid-to-freemium-how He is checking the product's Json info to confirm if a user owns the app by purchasing.
For subscription add-on related information, please check: https://learn.microsoft.com/en-us/windows/uwp/monetize/enable-subscription-add-ons-for-your-app
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