Players can earn up to a maximum of 75 Keys. When you reach the maximum limit, you will see the words "Max" flash on your Keys icon.
To see the Keys icon, tap on the House Icon at the bottom of your screen. Your Keys will appear in the top right corner when you're on the Challenges tab.
Please Note: If you purchase Keys from the Premium Store, your Key amount can go higher than 75. Tap on the Keys icon to purchase more Keys in the Premium Store.