Brick
From Castle Wiki
Bricks are Castle's in-app currency.
It's free to play and create decks with Castle, but there are some extra features you can unlock with bricks.
Getting bricks
The only way to get bricks is to buy them through Apple/Google in-app purchase.
To buy bricks, go to your Inventory, press the bricks icon, then press Purchase bricks to open the Market.
To view your current bricks balance, go to your inventory.
Exchanging bricks
Bricks can be exchanged for extra pin slots on your public profile.
To exchange bricks, go to the Market. You can either reach the market from your inventory, or you can go to the pin slots menu and press get more pins.