There are situations that require repayment, such as 1. You are useless this month, but you have handled the installment before, and the installment amount will be recorded in one month's account, so you still have to pay it back even if it doesn't cost money. 2. You didn't spend money this month, but you overdrawn last month and paid it back on the due date. Overdraft withdrawal shall bear interest on a daily basis, and the interest shall be compounded monthly. So this month's bill contains some interest, which will be paid back when it is due. You didn't spend money this month, maybe you didn't pay it all back last month. Then the remaining unpaid amount and interest are included in this month's bill, and you can continue to pay it later.