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.