Get Invoices Items using Deluge or API

Get Invoices Items using Deluge or API

I need to get item list when a new invoice is created. 
i need this because it is mandatory to integrate to government tax service.

I created a task that execute each time a new invoice is created, but I cant get item list from new invoice.

I try using webhook and Custom functions.

Using Custom function I tried:

  1. "invoice.get("item_list")", but item_list or similar is not available at response.
  2. zoho.invoice.getRecords("invoices","org_id","INV-000011"). It returns generic information about invoice but I can't find the list of items in invoice
where I could get the list of items sold in an invoice?

Thanks
Seba