Once you've selected the plan that works best for you, you'll need to set up a payment method in the billing portal.
To do this, simply stay on the Plans page and scroll to the right. DO NOT click on the Payment Info Tab. If you do, your payment method will not save properly when input on this page.
NOTE: In some instances you may not see the checkout cart on the plans page right away. This is because you need to scroll over to the right of the page to reveal it.