It appears from the documentation found here, that you can set your item parameters in the event parameters section. It should look something like .

Here’s an example of how it could be structured in the variable:

[
    {
      item_id: "SKU_12345",
      item_name: "Stan and Friends Tee",
      affiliation: "Google Merchandise Store",
      coupon: "SUMMER_FUN",
      discount: 2.22,
      index: 0,
      item_brand: "Google",
      item_category: "Apparel",
      item_category2: "Adult",
      item_category3: "Shirts",
      item_category4: "Crew",
      item_category5: "Short sleeve",
      item_list_id: "related_products",
      item_list_name: "Related Products",
      item_variant: "green",
      location_id: "ChIJIQBpAG2ahYAR_6128GcTUEo",
      price: 9.99,
      quantity: 1
    }
]

It seems more straightforward than you’d think, right?