All purchases in the game are processed by your app store (iTunes, Google Play and Amazon). If you're concerned about accidental in-app purchases, you can turn them off on your device or change the password used to make purchases in your app store account settings.
Please read the following articles to set up purchase restrictions on your device:
If you don't want to restrict in-app purchases completely, we suggest configuring your app store account to require a password for every purchase.