By targeting a campaign based on the Product/Variant ID within a users cart (available only for Shopify/BigCommerce) you can incentivize customers who are already in the buying mindset, to add additional items to their cart prior to finalizing their purchase.
Create your campaign using a no-form display and change the text on a button to say "Add to Cart". Next you’ll want to insert the add to cart link for each button. This link will automatically add the item to a shoppers cart when clicked.
For Shopify stores: When you insert the link, you just need to use a special permalink that includes your store URL, cart, the Variant ID, and the quantity. (Need help finding your Shopify Product or Variant ID? Click here)
For example: http://my-store.com/cart/add?id=123456789&quantity=1
Note: These targeting rules require product IDs found in your store admin. Do not enter a product SKU, product UPC, ISBN, GTIN, or MPN.
Finding Product and Variant IDs
Shopify: In your store admin, the product ID is the number at the end of the URL:
https://my-shop-name.myshopify.com/admin/products/791608229930
To get variant IDs, see https://help.shopify.com/en/themes/customization/products/variants/find-variant-id
Bigcommerce: In your store admin, the product ID is the number near the end of the URL:
https://store-name.mybigcommerce.com/manage/products/1234567890/edit