I've installed a custom module from Odoo store which automatically creates a credit note for returned products but this module gets the price from the product form which may not include the price on orders.

I need to change the value of price on each line to be calculated from the order line even if it is on sale or purchased.

This is the create method:

    @api.multi   
    def create_refund_invoice(self):   
    inv_obj = self.env['account.invoice']
    for pick in self.filtered(lambda x:x.return_type):
        type = 'in_refund' if pick.return_type == 'purchase' else 'out_refund'
        inv_lines = {'type':type, 'partner_id':pick.partner_id.id, 'invoice_line_ids':[]}
        account = pick.return_type == 'sale' and pick.partner_id.property_account_receivable_id.id or pick.partner_id.property_account_payable_id.id
        inv_lines['account_id'] = account
        inv_lines['origin'] = pick.name
        inv_lines['name'] = pick.origin
        for line in pick.move_lines:
            name = line.product_id.partner_ref
            pricelist_id = pick.partner_id.property_product_pricelist
            price = pricelist_id.get_product_price(line.product_id, 1, pick.partner_id) if pricelist_id else line.product_id.lst_price
            # price = pricelist_id.get_product_price(line.product_id, 1, pick.partner_id) if pricelist_id else line.product_id.lst_price
            # price = line.env['purchase.order'].search([('name','=',line.group_id)]).order_line.price_unit
            # price = line.move_lines.sale_line_id.price_unit

            inv_lines['invoice_line_ids'] += [(0, None, {'product_id':line.product_id.id,
                                   'name':name,
                                   'quantity':line.quantity_done,
                                   'price_unit': price,
                                   'account_id':line.product_id.product_tmpl_id.get_product_accounts()['income'].id})]
        if inv_lines['invoice_line_ids']:
            inv_id = inv_obj.create(inv_lines)
            pick.invoice_id = inv_id.id

What should I do ? I tried to set the

          price = line.env['purchase.order'].search([('name','=',line.group_id)]).order_line.price_unit

but it makes the price = 0

Any help will be appreciated.