I recently released a paid version of my application and received several downloads. One user requested a refund, and the refund was successfully processed by Google itself. He must have copied the apk and could share it with his friends using ShareIt or other apk sharing apps.
Now my question is , how can I check inside the application if the user bought the application or apk was just sent by someone else?
Hope my question is clear. Please fill in your advice / suggestions / experience / solution.
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