Cart button: "No items found"

I have a simple landing page on which I’d like to sell a digital product download. After publishing and clicking the “Buy eBook Bundle” button I get a “No items found”.

It seems to me it may be because its just the cart button and not an “add to cart” button? However I can’t add the “add to cart” button on landing page (seems I can only add on product page). Does that mean my product page needs be my landing page??

Any guidance here will be much appreciated. Read-only link below. Thanks!