In my case at least, I tested in both Chrome (my default) and Microsoft Edge (on Windows 10). Neither worked initially. Once I opened a new tab in chrome, logged into paypal on that and then clicked again on the button on BB, it worked for me.
My initial thought was that you needed to be actively logged into paypal, but I just clicked on the button now and it worked fine. Maybe something on their end changed recently and you need to sign into paypal once to have your account settings update? Or maybe they were just intermittently down, but now that I finally found where their notifications page was, the only thing I can find that's close is some problems with their REST APIs that they marked resolved on 3/30, and I think that was in the developer sandbox.