Every hoolah account will require you to set a default debit/credit card and all your automatic hoolah payments will be deducted from that card by default. If there is only one card added in your hoolah account, it will be the set as the default card.
If the card used to make payment for the 1st installment is different from the default card, the subsequent installment payment will still be deducted from the set default card.
You will not be able to delete this card unless you have added another card. There needs to have at least one card to be in your active account.