The product costs are implicit costs. This means that no money is actually debited from your cash account for these costs. The costs are charged as a reduction in value, which has an impact on the price of the derivative. However, these only become relevant if you hold the derivative for a long period of time.
When you buy a derivative, the purchase price x units + €1 flat-rate third-party costs are deducted from your cash account. The product costs are therefore not deducted directly from your credit balance on your settlement account.
All further information on the costs and the structure of the respective derivatives can be found in the basic information sheet.