Hello! I want to pop a window (ir.actions.act_window) on the @api.onchange when the user selects a product on a sale.order.line. The problem is that i get no error, but there is no window poping up.

Here is my code on sale.order.line: 

class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'
    @api.onchange('product_id')
    def check_product_qty(self):
        if self.product_id:
            self.open_back_order_window(self.product_id)
    @api.multi
    def open_back_order_window(self, product_id):
        vals = {'product_id': product_id}
        view_id = self.env['back.order.product.wizard']
        new = view_id.create(vals)
        form = self.env.ref('module.back_order_product_wizard', False)
        return {
            'type': 'ir.actions.act_window',
            'name': _('Warning : This product is not available at the moment'),
            'res_model': 'back.order.product.wizard',
            'res_id': new.id,
            'view_type': 'form',
            'view_mode': 'form',
            'views': [(form.id, 'form')],
            'view_id': form.id,
            'context': vals,
            'target': 'new',
        }

Here is the code in my wizard: 

from odoo import _, api, fields, models
class BackOrderProductWizard(models.TransientModel):
    _name = 'back.order.product.wizard'
    alternative_product_ids = fields.Many2many('product.template', string=_('Replacements products'))
    @api.multi
    def choose_product(self):
        pass

Here is the form im trying to show in a window:

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record model="ir.ui.view" id="back_order_product_wizard">
        <field name="name">Choose an alternative product when the one selected is B/O</field>
        <field name="model">back.order.product.wizard</field>
        <field name="type">form</field>
        <field name="arch" type="xml">
            <form>
                <group>
                    <span>The product you selected is not available. Please choose an alternative product</span>
                </group>
                <group>
                    <field name="alternative_product_ids"/>
                </group>
                <footer>
                    <button string="Cancel" special="cancel" class="oe_highlight"/>
                    <button name="choose_product" string="Choose product" type="object" class="oe_highlight"/>
                </footer>
            </form>
        </field>
    </record>
</odoo>