I am not able to call wizard on sales order onchange method

Here is my View.xml:

<record model="ir.ui.view" id="wizard_form_view">

    <field name="name">Wizard Form</field>

    <field name="model">stages.wizard</field>

    <field name="arch" type="xml">

        <form string="Email Confirmation">

                <field name="message"/>

        </form>

    </field>

  </record>

Here is my wizard.py:

class wizard(models.TransientModel):

    _name = 'stages.wizard'

    message = fields.Text("Message")

Here I am calling wizard in onchange method:

@api.constrains ('so_stage')

    @api.onchange ('so_stage')

    def _onchange_so_stage_name(self):

        string_error = ""

        so_order = self.name

        return {

            'type': 'ir.actions.act_window',

            'res_model': 'stages.wizard',

            'view_id' : 'wizard_form_view',

            'view_ref' : 'wizard_form_view',

            'view_type': 'form',

            'view_mode': 'form',

            'target': 'new',

        }

After onchange method triggered the wizard does not pop up.