Prepare

1. open themes/advanced/in-commerce/elements/products.elm.tpl file for editing
2. in the product_element block above the line with AddToCartLink tag usage add <inp2:m_Set {$PrefixSpecial}_id="1"/> code
3. save changes

Testing

1. Go to Admin Console, Website & Content → Structure & Data → Products.
2. Switch to the Products tab.
3. Create a couple of the products, when there are none (goal is to have 2 products at least)
4. Go to Front-End, Products.
5. Click on the Buy now link on 1st of the products in the main list (right part of the page)
6. Confirm that you redirected to the shopping cart with your chosen product added
7. Click on the Buy now link on 2nd of the products in the main list (right part of the page)
8. Confirm that you redirected to the shopping cart with your chosen product added