For security reason, we accept only verified and confirmed PayPal accounts. Looks like although your business account is verified, you seem have not confirmed your PayPal email address yet. Please follow the instruction in this link (https://www.x.com/developers/community/blogs/ppintegrationsnate/confirm-your-paypal-email- address) to confirm your email address. Once your PayPal email address is successfully confirmed, you should be able to register it to your FormsCentral account.
Please let us know if that fixes your problem, and surely don't hesitate to contact us if you have further issues.