We only charge your card for the first installment when you complete your order and pay successfully.
At that time, the order amount is set, and any remaining amount requested but not used drops off.
Your first installment is charged for 25% of the total order amount to your debit card linked to your QuadPay account, and any remaining authorization amount is voided.
For example, if you request a purchase for $120, but only spend $100 when you check out, the remaining $20 isn't charged and is made available in your limit for future requests again right away. Your first installment of $25 is charged to your linked debit card, and $25 will be charged every 2 weeks until your order is paid off (for 4 installments total).