None. The app makes no network requests of its own. Your flip statistics and settings are stored only on your device; deleting the app removes them.
Optional tips are processed by Apple; they unlock nothing. We never see your payment details.
The app does not knowingly collect data from anyone, including children.
If a future version changes how data is handled, this page and its date will be updated and any data-collecting feature will be opt-in and disclosed in the App Store privacy details.
Questions about this policy: dautovri@outlook.com.