Shopify - how to serach by product variation

I have an underwear and Bra shopify website:
I wish to search by the product variation ‘size’ and return all products with the size entered and a stock level > 0
Eg if I enter 12D I would like to see all ‘available’ products in size = 12D
At the moment, when I look at my search results, there are products with the size of 12D, however they are out of stock!
For instance, this product is in the results after I enter 12D, but when I drill down, there is no stock in size 12D
Can anyone help please?

I don’t think that Algolia is returning the product you linked to (the Gel convertible black one).
As you can see on this screenshot:

Algolia is enabled in your autocomplete menu, but not on your search page (when you press Enter).

To enable it, you need to:

  • Head to the Display tab of our app
  • Head to the Instant Search page section
  • Enable instant search
  • Set the CSS selector to a value that works for your website
    See for more information
    In your case, I believe .container (with the dot) would work just fine.
  • Save and reload your search page