WHMCS Tags troubleshooting-article Troubleshoot and resolve unexpected changes to a service's Next Due Date value. Troubleshoot and resolve issues with customers receiving unexpected subscription cancellation emails from PayPal®. The system is unexpectedly suspending services (for example, hosting accounts). The system is unexpectedly terminating services (for example, hosting accounts). Troubleshoot and resolve unexplained declined cards and failures. Troubleshoot and resolve transactions that the system isn't recording. 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.