Your funds
Your two balances: fourdigits Wallet and Free Reward Wallet
Your account shows two balances side by side. One is money you can withdraw; the other is reward credit for tickets. How each is filled, spent and kept.

The fourdigits Wallet
This is your money. Deposits land here, and so do all your winnings, whichever balance paid for the ticket. It can buy tickets and it can be withdrawn at any time to an address you have saved, subject only to the withdrawal fee shown on the Withdraw screen.
The Free Reward Wallet
This holds rewards, such as the one paid when a friend joins with your link. Reward credit buys tickets exactly like cash, but it cannot be withdrawn as it is. Think of it as tickets waiting to be used rather than as money in the bank.
Which pays for a ticket
When you buy a ticket, the quote shows how much of it each balance will pay, for example part from rewards and part from your wallet. You see the split before you confirm, so there are never surprises about which balance went down.
Where winnings go
Every prize is paid into your fourdigits Wallet, including prizes on tickets bought with reward credit. That is the point of rewards: they give you tickets to play, and anything those tickets win becomes real, withdrawable money.