Ok - I guess the problem is that you have to create a transaction to the Ethereum network to redeem the winnings. Although you don't have to send any money in this transaction the transaction itself costs some fees (gas/Ether). For now you need to have this amount upfront on your account.
We will work on a solution so that the transaction fee can be paid from the amount you earn by redeeming your winnings. However - in this case a third party has to do the transaction and pay the transaction fee upfront. We will most likely do it in a future version. For now you account must at least hold something like 0.05ETH - or 0.1 so be safe to do the transaction.