If you have downloaded World Flipper from the Google Play Store,
you can set a purchase password to avoid any unintended purchases.
How to Set Google Play Store Purchase Password
1. Open Google Play Store and select the "Menu (≡)" icon on the top.
2. Select "Require authentication for purchases" from Settings.
3. Select "For all purchases through Google Play on this device" option.
4. Set a purchase password for your google account.