You cannot add this bundle to the cart.

Hi, im emiliano.
There is a strange behaviour when i try to use “buy now” button instead add to cart button.
You can see this strange behaviour in this link and click on “Acquista subito”.
https://www.simplyeasier.it/simply-packs/rocket-pod/

When i click on “Acquista subito” this message appears : you cannot add this bundle to the cart.
on the bundle slot appears a product that is not selected AND is out of stock. Why ?
Please show the attachment.
Can you help me please?
thanks
Emiliano