Yes. At the time of booking any remaining funds required to cover the cost of the offer, beyond what's taken in the card payment, will be taken from your Duffel balance. It is your responsibility to ensure you have enough money in your Duffel balance to cover the total price of the offer or the order will fail to go through.
You can do this by topping up your balance via bank transfer.
You will receive notifications if your balance is low.