Sell eBooks in the same page with hard-copies

-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.8.2
-- PHP version -- : 7.0.20

Hi!
I want to sell books in both physical and digital form. I also want to sell them on the same page.
What I have done so far is to create the product with 2 variants so the customer can choose between ebook or hardcopy.
The problem is that when customer orders an ebook, during checkout hikashop asks about postage.
How can I disable postage in ebooks?

Thanks in advance
Vasilis

It works!

Thank you!