Hi,

In the existing code in the automation for creating invoices you can modify it like this:

The "lines" are the invoice lines. In the dictionary, you can add the appropriate values. like in the product_id you can add the id of specific product.

And the lines are used in the invoice creation as invoice_line_ids. It will create the invoice lines too.

def action_create_invoice_line(self):
        lines = [(0, 0, {
            'product_id': product_id.id,
            'name': description,
            'quantity': 1.0,
            'price_unit': price,
        }) for rec in self]
        invoice = self.env['account.move'].create({
            'move_type': 'out_invoice',
            'partner_id': partner_id.id,
            'payment_reference': reference,
            'invoice_date': (datetime.now()).date(),
            'invoice_line_ids': lines
        })

Regards