This is a common issue that occurs during WordPress theme installation. The reason you are getting this error message is that you are trying to upload the incorrect file, that is, you
The Demo Importer will start only after you install and activate the child theme. Demo Importer will not work with the installed and activated parent theme.
Installing a WordPress theme is just as quick and easy as installing WordPress. (If you haven’t installed WordPress already, you can do so by following the official WordPress guide.) Themes Kingdom WordPress