No Free Product in waiting list

Hi,

Are you sure you're talking about the waiting list, not the wishlist ?
The waitlist is for when the product is out of stock and there is no way for the user to check his waiting list from the frontend. It can only be checked in the backend.
So I suppose you're talking about the wishlist.
And I suppose that your issue is linked to the "display add to cart button for free products" setting of the Hikashop configuration.
If that setting is turned off it will remove the add to cart AND add to wishlist buttons on the products without a price.

Turning on that setting would of course display the add to wishlist button for the free products, but I suppose you don't want the add to cart button for these products.
In that case, what you could do is to use the "like" plugin we have on our marketplace instead of the wishlist system:
www.hikashop.com/marketplace/product/155-product-like-btn.html
It's basically similar to the wishlist but for different purposes. The wishlist system is useful to have more complex lists, like weeding lists, baby showers, that you can share with others. The like system is more lightweight. It just allows you to like / unlike products and only you can see the products you liked. And you can create a products listing menu item listing all the liked products thanks to the "liked products" setting of the menu item.