WHMCS Tags troubleshooting-article Troubleshoot and resolve issues with customers receiving unexpected subscription cancellation emails from PayPal®. Troubleshoot and resolve The sender's email address is not registered. (WHMCS 8.4 and later) or Unregistered Email Address (WHMCS 8.3 and earlier) errors. Troubleshoot and resolve IP Address prohibited errors while using WebNIC for domain registrations. Troubleshoot and resolve Wrong logon name or password. Please try again errors while using WebNIC for domain registrations. Troubleshoot and resolve IPartner authentication failure errors while using WebNIC for domain registrations. Troubleshoot and resolve Whoops Exception Maximum execution time of 30 seconds exceeded errors.