Up-Sells window is not showing up

Hello, I´ve bought and successfully installed the plugin, I´ve tried to activate the up-sell popup without success. I´ve been to “WooCommerce> Settings > Products > Display > Add to cart behavior, untick on Redirect to the cart page after successful addition” (actually redone) und set up as described in documentation. There inst any window showing up after i click “add to cart” and there are no further instructions. Can u please give support. Domain is: http://www.hufoel.at .