We know that the payment screen has a few quirks and we’re working to get them out. You may run into a situation where you have added all required fields but you still cannot click the ‘Proceed’ button. This is a known glitch, but luckily is pretty easy to resolve.
Close out of the payment screen, then click to purchase again. When you enter your information this time, make sure you enter it in the order the fields are presented. We have observed that for some people, if they enter their credit card information before they enter their billing address, the Proceed button will not activate.