For any customization requests you can open a “custom work” ticket via the support site by clicking here.
One of the most common reasons people have issues is because they try uploading the full zip that includes demo content, theme, documentation…etc which creates the error “The package could not be installed. The theme is missing the style.css stylesheet.”. Please make sure you are uploading only the installable theme which is called cariera.zip.
More Info: here
You can use 1 license for 1 domain. If you want to use the theme on a 2nd website you will have to buy another license.