products don’t added

Hi.

Yesterday my colleague Alessandro Bergamin bought your extension.

I add the funnel in my checkout page.
I see the upsell products but when I click one ore more of these products, they’re no added in the cart.
See this video: https://screencast-o-matic.com/watch/crQuXPV6GrR

I create this test product: https://www.topmodelfit.it/prodotto/test-ignore/ (the site is live, so the upsell funnel is active only in this product that is hide in the shop).
You can add this product in the cart and try.

Can you help me please?

Thanks.