While Badland Brawl is free to play, you also have the option to purchase in game currency to progress faster.
To set restrictions on your Samsung Galaxy App please follow these steps:

1. Start the Samsung Galaxy Apps, and got to the "Settings" menu.   
2. Look for “Purchase protection”. 
3. Enter your password, and confirm.    

From now on, you will be asked for your password whenever you want to make a purchase.