You have enabled generation of Google Shopping XML Product Review feed in the settings of the plugin. However, no XML file is created. The folder is empty and when you try to access URL of the XML feed in a browser, error 404 (not found) is shown.
This problem is most likely caused by the missing 'write' permission for the folder where the plugin saves the XML feed. Please make sure that WordPress has the permission to create and change files in the folder where the plugin saves the XML feed. After you added the missing permissions in the file system of your web server, re-save the settings in the plugin to re-generate the XML feed.