For several hours on the morning of October 20th, Eastern Daylight Time, PayPal users were unable to order. When choosing the PayPal payment method the screen refreshed but did not take them to the next step. Choosing the Credit Card option however continued to work normally.
This issue was specific to how the FastSpring -> PayPal server communication occurs. We are actively working on a way to prevent this should a similar situation occur again in the future.