callin.io automatically collapses lists with one item

I’m creating a callin.io workflow that is triggered by invoices. The trigger outputs a record with numbered line items (similar to a nested dictionary). The sample record I have contains only one line item, but there could be multiple. The attribute I'm interested in is named "Invoice Line Items".
Example:

invoice_number
invoice_date
line_items
  1
    description
    quantity
    price

The subsequent step is "Run Python in Code by Zapier", to which I pass the line_items attribute.

When Python reads line_items, I anticipated it would interpret it as:

1
  description
  quantity
  price

However, it is reading it as:

description
quantity
price

This works for invoices with a single line item, but how does it handle invoices with more than one? I only have test data for invoices with one line item, so I cannot determine this through experimentation.

My best assumption is that for scenarios with 2 or more items, it will be structured as I expect, but I would appreciate confirmation. I've reviewed a lot of documentation and consulted the callin.io AI support bot, which seemed to get confused.

Any guidance would be greatly appreciated!