Display add to cart button on a per product base

Hi,

One option is to not have a price for these products and turn off the "display add to cart button for free products" setting of the HikaShop configuration.
Another option is to set the "quantity" (stock) of the product to zero. This will display an "out of stock" message for these products instead of the add to cart button. You can use a translation override of that text in order to change it to adapt it to your situation:
www.hikashop.com/download/languages.html#modify

If you want to apply these to a bunch of products at once, you can select them on the products listing, click on the "actions" button, and in the popup, you can use the action "update the values" to modify all the products at once.
For example, you could apply the action on the "product_quantity" column, with the value "0" to make all the selected products out of stock at once.

Hi,

If the stock of the main product is set to zero, and the variants have a stock set to unlimited, the variants will automatically use the stock of the main product as their own stock and thus, the variants will also be out of stock.
And if the "display out of stock products" setting is deactivated in the HikaShop configuration, the variants without stock will be removed automatically from the product page, which will lead to the "no values found" error because the system sees that you have characteristics for the product, but no variants available for the product. And thus a selector cannot be generated.
I suspect that this is your situation.