The failed request tracing feature assists you in troubleshooting issues with your websites by making IIS failed request files available in the Plesk interface. The failed request files contain information such as the requested URL, relevant application pool name, the HTTP status code, and more.
To view the list of all failed requests files created so far, go to the Websites and Domains tab > Failed Requests Tracing. You can click any of the failed requests files to view their contents; you can also download one or more files packed into a ZIP archive, or remove the files that are no longer necessary. You can start a new trace by specifying one or more HTTP status codes and the IIS component or components for which failed request files will be created. Once a trace is started, you can change these settings at any time.