Hi,
i'm learning Odoo and I want to create gantt view on Odoo 18.

I got this error: 

TypeError: 'set' object is not subscriptable

Here's my code

<odoo>

    <!-- View: Training Schedule Gantt -->
    <record id="view_training_gantt" model="ir.ui.view">
        <field name="name">stable.training.gantt</field>
        <field name="model">stable.training</field>
        <field name="arch" type="xml">
            <gantt string="Training Schedule"
                   date_start="start_date"
                   date_stop="end_date"
                   color="color"
                   progress="progress"
                   default_scale="day"
                   duration="duration"
                   quick_create="1">
                <field name="horse_id"/>
                <field name="start_date"/>
                <field name="end_date"/>
                <field name="progress"/>
                <field name="duration"/>
                <field name="assigned_to"/>
                <field name="color" widget="color"/>
            </gantt>
        </field>
    </record>

    <!-- Action: Open Training Schedule -->
    <record id="open_training_schedule_action" model="ir.actions.act_window">
        <field name="name">Training Schedule</field>
        <field name="res_model">stable.training</field>
        <field name="view_mode">list,form,gantt</field>
    </record>

    <!-- Menu Item: Training Schedule -->
    <menuitem id="menu_training_schedule"
              name="Training Schedule"
              parent="menu_stable"
              action="open_training_schedule_action"
              sequence="20"/>
</odoo>

I don't understand my error. 
Need help please

Thank you
Here's the tuto: cybrosys.com/blog/how-to-create-gantt-view-in-odoo-18