services.xml

    <service id="App\Promotion\Action\FreeItemPromotionActionCommand">
        <tag name="sylius.promotion_action" type="free_item" label="app.form.promotion_action.free_item" form-type="App\Form\Type\Promotion\Action\FreeItemConfigurationType" />
    </service>

services.yaml

    App\Promotion\Action\FreeItemPromotionActionCommand:
        tags:
            - { 
                name: sylius.promotion_action, 
                type: free_item, 
                label: 'app.form.promotion_action.free_item', 
                form_type: App\Form\Type\Promotion\Action\FreeItemConfigurationType 
            }