Paypal button not working in Pro Sites

I have set up a Pro Sites level where people can purchase it using Paypal Express. I upgraded my Paypal account to Business and connected using the API credentials that I was provided. Everything runs smoothly until a user attempts to click the Paypal button to make a purchase. This button is failing to redirect to the Paypal payment screen. Instead it refreshes the current screen.

I just got off the phone with Paypal and confirmed that my account is set up correctly and that my API credentials are correctly configured. They logged into a test subdomain in my network and were able to duplicate the problem for themselves.

Please advise!