Hi @suryainno!
It’s actually expected behavior for Klaviyo to only read top-level attributes, so the only way to accomplish this would be to implement some sort of custom solution. One potential solution that comes to mind would be to create a separate custom event that is triggered alongside the “Order Confirmation” event, but contains a top-level attribute that corresponds to the product_line_items array.
However, this would be a custom project that would be beyond the scope of support/community, so you’re always welcome to reach out to one of our wonderful Official Partners for further development help.
Best,
Brian