You can purchase in-game items from the in-game Store, using real world currency from your Steam Wallet. For more information on Steam Wallet, check out Steam support.

Steam Overlay is required for in-game purchases. Attempts to make an in-game purchase without it enabled will result in a "Transaction in Progress" error message.

For steps on enabling Steam Overlay, view this Steam support guide.

In-game purchases, including items you unlock with Marks of Fortune are nonrefundable.