How do I restrict in-app purchases on my Android device?

• Google has a good few ways of ensuring that your device is protected against unintended purchases, and the best way is requiring a password before any purchase can be made. 
  
  • Open the Google Play Store on your device.
  • Tap the Menu (the three lines) on the left side of the search bar.
  • Scroll down to Settings.
  • Select the Require Authentication For Purchases option.
  • Ensure the first option, indicating all purchases, is selected.
  • When setting this up or disabling it, Google will usually ask for your account password.
  Automatic In-App Purchases are now disabled and a password will be required to enable purchases on your device.
  
• How to use your fingerprint scanner for purchase authentication
  
  • Open up the Google Play Store on your device.
  • Tap the Menu (the three lines) on the left side of the search bar.
  • Scroll down to Settings.
  • Select the Require Authentication For Purchases option.
  • You need to make sure you select the first option. That’s how you apply the setting to all purchases.
  • When setting this up or disabling it, Google will usually ask for your account password.