When paying with your Duffel Balance, you'll need to have enough money to cover the cost of the booking. If you don't, you'll have to top up.
If you're paying for flights using your Duffel Balance, you'll need to have enough money deposited to cover the cost of the booking. If you don't, you won't be able to create your order until you top up.
You can keep track of the balance of your balance from your dashboard. You can also configure the threshold that will be used to send you a low balance notification.