If you get the “The theme is missing the style.css stylesheet” error message from WordPress, you try to upload the wrong folder / zip file. Please make sure that inside the file you upload is only the theme.
Sometimes we have to set up the zip files on different marketplaces with the demo content and the documentation in one zip file, together with the theme. In this case, please unzip first the downloaded zip file and upload only the theme. Normally you can see directly what is the theme and what is the demo content or the documentation.