Using on other platform

I want to purchase one item from Marketplace. But in supported platform on this product selected just Windows. I developing on MacOS. And author of product wrote what e dont using Windows-specific features, just common Epic animations tools and blueprints. But before purchasing UE4 write what I can not run and download this product on my platform. How I can download it after purchasing? Is it impossible? I must find Windows?

It may depend on the item (some code plugins may be Windows only), but for the most part you will probably be fine; it means that the author cannot guarantee that that item will work. If in doubt, contact the author directly.