Instead of choosing the "pay now" option at the bottom of the screen, go to the menu on the left side and select "make payments".
You will have 2 options, "on demand" or "immediate".
"On demand" allows you to store your credit card information so you don’t have to enter it each time you want to make a payment.
If you choose "immediate", this is a 1-time only payment and does not store any credit card information.
If your credit card information has already been saved, the last 4 digits of the card number will appear and you can select "make payment" next to the card number. If not, you can add the information and it will be saved for the next time you make a payment.