Are you using safari and checking out with PayPal?   Is so we are working to resolve this as Safari can block popups from firing which means users cannot see the PayPal window. If you allow popups from your device by going to Settings > Safari > Block Pop-ups > Yes you can then checkout via PayPal from the checkout page.   We apologize for any inconvenience and appreciate your patience while we work with PayPal to resolve this issue.   

If you are experiencing a similar issue please let us know if you are on a moblie/tablet or a desktop devise, what broswer you are using and if you are checkout with PayPal.  Screen Shots are always welcome so we can attempt to resolve your issues more quickly.