WHMCS Troubleshooting Troubleshoot Payments Troubleshoot and resolve processing issues that did not result in a log entry. Troubleshoot and resolve an Oops Error: Module Not Found error. Troubleshoot and resolve problems due to PayPal® Instant Payment Notification (IPN) failures. PayPal payment gateways may generate specific subscription log entries. After attempting to migrate to the new PayPal Payments payment gateway module from a previous PayPal® module, you are experiencing problems with subscriptions. Troubleshoot and resolve PayPal connection errors. Troubleshoot and resolve Transaction ID already exists errors for PayPal Payments transactions.