For iOS players, if you'd like to disable or enable the possibility of making in-app purchases, or if you want to control the levels of security for each step of the purchasing process, simply follow the steps below:
• Head over to your device's Settings
• Select 'General' and then 'Restrictions'.
• Enter your passcode if you wish to enable the restrictions.
• Scroll down to In-App Purchases and choose to completely disable every in-app purchase (turn the settings to OFF). Alternatively, you can manage the frequency of the password request using the Require Password button.
• If you want to keep the ability to make in-app purchases, you can set the device to require your password every time you make a purchase.
For Android players, check Edit your payment method - Google Play
For Windows/ Windows Phone players, check How to edit payment method for the Windows store and view billing history