How to assign free shipping only to a product category?

[Nican]

Hello,

I have a product category which I have assigned free shipping (using cart rules)

 

Everything is fine if I purchase just some products from this category,

but as soon as I add a product from a differet category,

the shipping stays free, instead that calculating shipping fees

for the new products

 

I tried a workaround not using cart rules, assigning a free courier to those products I want to ship for free,

but still when I add to my cart some products from a different category, the shipping stays free,

meaning that prestashop seems not to able to assign different couriers to different products in the cart,

 

it just takes the courier of the first product (if that product has just one product disposable) and it uses it 

for all the other products

 

Anyone has any idea on how to solve this?

Thanks!