Once you select the number of people from the Quantity dropdown and enter your contact info, click on "Continue". The "Pay with Paypal" window will show up. Click on Place Order. If you don't have a Paypal account, you can still pay using your credit card by simply clicking "Pay with a credit or Visa Debit card" option at the bottom.
Once you click on it, you will be able to enter the required info for checkout. See screenshots below.