Your first payment won't be due until the end of the next month. When you open your account, Zip will set up a monthly payment of $40 (or less if the amount you owe is under $40). This will come from your linked credit card on the last day of each month and run until your purchases are paid off.
Finally, if there's nothing owing on your account, there's nothing to pay. Your account simply remains active until you're ready to make a purchase.
For more Zip FAQs, please visit https://help.zip.co/en