I can't upgrade to pro either.
PayPal causes NZB360 to stop. I have removed paypal app and re-installed nzb360. Still FCs. Pay by card is greyed out for me.
I can't upgrade either. I can't even get the page with the paypal and cc option to load fully. I hit the upgrade button, it asks me what email to associate the app to, I click my email address, then I see the CC and Paypal button briefly before it disappears, and goes back to the previous screen with the upgrade graphic and then crashes/stops. I have uninstalled the PayPal app and deleted its temp files and restarted the phone. no help.