Verify payment gateway configuration settings, Ensure API credentials are correct, Check for compatibility issues with OpenCart version, Look for errors in the server logs or payment gateway logs.
Check the database for missing order entries, Verify the order statuses and filters in the admin panel, Ensure the correct permissions are set for viewing orders.
Review shipping extension settings, Check for conflicting shipping methods, Update or reinstall the shipping extension if necessary.
Enable error reporting in the config.php file to display errors, Ensure all files are uploaded correctly and not corrupted, Look for compatibility issues with themes or extensions.