To make a payment, use the quantity to select increments of $10 each. For instance, if you are making a $200 payment, change the quantity to 20. If you need to add amounts between $1 and $9, use the $1 payment item to add to your payment as though you are buying multiple things.

Note that when you check out you will be required to choose a shipping method which doesn't exactly make sense for a purchase of this nature. Just choose Free Shipping.