Invoice item is associated with invoice. It has the following fields
id: Unique id for the invoice item.
invoice_item_seq_id: A sequential id for the invoice line.
line_item_value: The total value of the line without taxes and with adjustments.
invoice: The invoice.
total_applied_tax: Total taxes for the line.
extended_price: The total value of the line with taxes and without adjustments.
unit_cost: Price per unit.
item_description: Description of the line.
amount: The amount entered for the line.
product: The product if the line is for a product. See product. This field is only set if the invoice item is not related to an order shipment or the invoice item is not converted from order. Use the associated_product would be the best way to obtain the related product to an invoice item.
order_shipments: A list of order shipments for the line.
organization_gl_account: The account that is used for recording revenue. Can be null.
measurement_unit: The unit used.
product_id: Id of the product the line is associated with. This is only present if the product is chosen when the invoice is created directly. If an invoice is created from an shipment, then id is blank. It is best to use associated_product to get the product related to the invoice item in all cases.
associated_product: Return a product related to the order.
cost_of_goods_sold: The cost as calculated.
line_item_value_without_adjustments: The total value of the line without taxes and without adjustments.
invoice_item_adjustments: A list of adjustments for the line.
order_item_invoicings: Related order item invoicing records. This is present if the invoice is generated by converting a sales order.
invoice_item_applied_taxes: A list of taxes that is on the line.
public_custom_fields_list: A list of custom fields.
order_items: A list of related order items.
lots_numbers: Lot number associated with the invoice if dealing with lotted products.
item_description_and_product_name: A helper method that combine item description on the invoice item to the name of the product.
voided: If the line is reversed (this applies to invoice adjustment lines only)