How can I add a variant to a coupon?

-- HikaShop version -- : 3.1.1
-- Joomla version -- : 3.7.5
-- PHP version -- : 7.0.22
-- Browser(s) name and version -- : Both latest Chrome and Firefox

I see that in version 3.1 the feature "You can now select variants for coupons and discounts and not only products" has been added. However, if I go to create a coupon code and want to restrict it to just one variant of a product, all I see in the listing is the entire product.

How do I select a single variant?

I tried multiple browsers in case I was just having an issue with the one I was using (Chrome), or if there was old code cached int he browser.

Any help would be appreciated.
Thanks.

I have partially answered my own question, however, I have found two issues with this.

I have found that the product can be expanded within the list to show the variants, but ONLY if navigate the category tree and find the product manually. If I start typing the name of the product, to filter the list so that I can find the product faster, it is not expandable. Given that I have a lot of product I always filter the list to make finding products faster.

The second issue is that I did end up selecting the variant properly for the coupon, but the coupon code can't be used. All I get is the error:

The coupon you entered cannot be used for the products in your cart

I have downloaded the latest installer and have installed it on my website. Unfortunately, it hasn't fixed either issue. If I filter the product list in the coupon page, I still don't see any way to choose a variant. Added to that the coupon code I do have for the variant still does not work even when the variant is in the cart.

Any other ideas?

I have redownloaded and installed again. It is now working properly. Thank you!

Nothing to clarify. It is working now. The fix that Nicolas posted worked perfectly.