A common issue that can occur while installing a Jupiter theme is “The package could not be installed. The theme is missing the style.css stylesheet.” This error message is displayed when uploading or activating the theme.
The reason may be that you tried uploading the full zip file that includes sample data, documentation, etc.
Please make sure you are uploading only the installable theme called Jupiter.zip.
When you download the theme from your ThemeForest downloads it will give you two choices: one is to download the full zip file which you will then need to extract in order to locate the theme and the other one is just the installable theme.