modifyAddressFields
The modifyAddressFields hook is triggered by “Billing Address” and “Shipping Address”
checkout steps. Each checkout step triggers the hook twice – first when address form is
being rendered, then upon submit when fields are validated.
It can be used to modify fields configuration, add or remove fields, or do something with the submitted values.
Parameters
- 
array
$fieldsArray of form fields configurations (similar to DCA).
 - 
\Isotope\Model\Address
$addressInstance of the Address model.
 - 
string
$classStandardized version of the current CheckoutStep class, that can be used in CSS context, e.g.
'billingaddress' 
Return value
Return the $fields array.
Example
// src/EventListener/Isotope/ModifyAddressFieldsListener.php
namespace App\EventListener\Isotope;
use Contao\Input;
use Isotope\Model\Address;
use Isotope\ServiceAnnotation\IsotopeHook;
/**
 * @IsotopeHook("modifyAddressFields")
 */
class ModifyAddressFieldsListener 
{
    public function __invoke(array $fields, Address $address, string $class): array
    {
        // Normalize email addresses to lower-case form
        if (Input::post('FORM_SUBMIT') === 'iso_mod_checkout_billingaddress') {
            Input::setPost('billingaddress_email', strtolower(Input::post('billingaddress_email')));
        }
        
        return $fields;
    }
}