Create a selector in the registration form and validate PrestaShop 1.6

I need to add a selector registration form and this data is stored both in the database and in the backoffice for the admin can see this information.

I found this guide, worked well, but I had some problems. The guide is specific to a text field and not for a selector.

When I try to register there is a validation error, says the selector field is mandatory, but actually if I chose an option

Here the link to the guide that I followed

My site is created with prestashop 1.6, with the theme Venedor

The site to see my progress is this (although only will be able to see the front end)

The code selector in authentication.php is below birthdate:

            <div class="required select form-group selector2">
                <label for="facturacion" class="i-additional f-label">{l s='Facturación'} <sup>*</sup></label>
                <select name="facturacion" id="facturacion" class="form-control">
                    <option value="">-</option>
                    <option value="Monotributista">Monotributista</option>
                    <option value="Responsable Inscripto">Responsable Inscripto</option>
                    <option value="Consumidor Final">Consumidor Final</option>
                    <option value="Excento">Excento</option>
                </select>
            </div>

Hope you can help me. thx