def METHOD_NAME(po, invoice_item_names):
	for item_name in invoice_item_names:
		invoice_item = frappe.get_doc("Invoice Item", item_name)
		po.append(
			"items",
			{
				"invoice_item": invoice_item.name,
				"invoice": invoice_item.parent,
				"document_type": invoice_item.document_type,
				"document_name": invoice_item.document_name,
				"rate": invoice_item.rate,
				"plan": invoice_item.plan,
				"quantity": invoice_item.quantity,
				"site": invoice_item.site,
			},
		)
	po.save()