Customer can't check out through PayPal on Pro Sites


My customer who want’s to sign up after a trial period is having problems checking out with PayPal.

This is her site:

When she clicks on the checkout button the page simply refreshes.

I have exactly the same issue when I create a site and then try and upgrade through PayPal as you can see here:

Please tell me how we can fix this issue as soon as possible.

It may be related to a similar issue being looked at:

Hope to hear soon.