Magento 2 customer custom attributes such as VAT

I am tring to add a customer custom attributes such as VAT.
So I will not use the address structure but account structure.
And i want to display the field during the payment and not during the first step (shipping info).
But the result is

This is the code

SetupInstallData.php

namespace VendorItalianFiscalAttributesSetup;
use MagentoFrameworkSetupInstallDataInterface;
use MagentoFrameworkSetupModuleDataSetupInterface;
use MagentoFrameworkSetupModuleContextInterface;
use MagentoCustomerModelCustomer;
use MagentoCustomerSetupCustomerSetupFactory;
use MagentoEavModelEntityAttributeSet as AttributeSet;
use MagentoEavModelEntityAttributeSetFactory as AttributeSetFactory;
/**
 * @codeCoverageIgnore
*/
class InstallData implements InstallDataInterface
{
private $_eavSetupFactory;
private $_attributeRepository;

/**
 * @var CustomerSetupFactory
 */
protected $customerSetupFactory;

/**
 * @var AttributeSetFactory
 */
private $attributeSetFactory;

public function __construct(
     MagentoEavSetupEavSetupFactory $eavSetupFactory, 
    CustomerSetupFactory $customerSetupFactory,
    AttributeSetFactory $attributeSetFactory,
    MagentoEavModelAttributeRepository $attributeRepository
)
{
    $this->_eavSetupFactory = $eavSetupFactory; // questa classe serve per costruire un attributo (prodotti , indirizzi, account ...)
    $this->customerSetupFactory = $customerSetupFactory;
    $this->_attributeRepository = $attributeRepository;
    $this->attributeSetFactory = $attributeSetFactory;

}


/**
 * {@inheritdoc}
 */
public function install(ModuleDataSetupInterface $setup, ModuleContextInterface $context)
{
    /** @var CustomerSetup $customerSetup */
    $customerSetup = $this->_eavSetupFactory->create(['setup' => $setup]);
    $customerSetupFac = $this->customerSetupFactory->create(['setup' => $setup]);

    $setup->startSetup();

    $customerEntity = $customerSetupFac->getEavConfig()->getEntityType('customer');
    $attributeSetId = $customerEntity->getDefaultAttributeSetId();

    /** @var $attributeSet AttributeSet */
    $attributeSet = $this->attributeSetFactory->create();
    $attributeGroupId = $attributeSet->getDefaultGroupId($attributeSetId);

    /* customer type è per identificare la tipologia di cliente privato italiano o azienda italiana 
     * in modo da capire se rendere obbligatori i campi fiscali e quali.
     * altro non li rende obbligatori
     */
    //customer fields
    $customerSetup->removeAttribute(Customer::ENTITY, 'customer_type');
    $customerSetup->addAttribute(Customer::ENTITY, 'customer_type', [
        'type' => 'text',
        'label' => 'Type of customer',
        'input' => 'multiselect',
        'class' => 'tipo_cliente',
        'frontend_class' => 'validate-tipo-cliente',
        'required' => false,
        'visible' => true,
        'user_defined' => true,
        'sort_order' => 01,
        'position' => 01,
        'system' => 0,
        'backend' => 'MagentoEavModelEntityAttributeBackendArrayBackend',
        'source' => 'VendorItalianFiscalAttributesModelEntityAttributeSourceTypeCustomer',
        'global'        => MagentoEavModelEntityAttributeScopedAttributeInterface::SCOPE_STORE
    ]);

       $used_in_forms[]="adminhtml_customer";
    $used_in_forms[]="checkout_register";
    $used_in_forms[]="customer_account_create";
    $used_in_forms[]="customer_account_edit";
    $used_in_forms[]="adminhtml_checkout";

    $customer_number = $customerSetupFac->getEavConfig()->getAttribute(Customer::ENTITY, 'customer_type');
    $customer_number
        ->setData("used_in_forms", $used_in_forms)
        ->setData("attribute_set_id", $attributeSetId)
        ->setData("attribute_group_id", $attributeGroupId)
        ->setData("is_used_for_customer_segment", true)
        ->setData("is_system", 0)
        ->setData("is_user_defined", 1)
        ->setData("is_visible", 1)
        ->setData("sort_order", 77);
    $customer_number->save();


    $setup->endSetup();
}}

etcmodule.xml

< ?xml version="1.0" ?>

etcfrontenddi.xml

< ?xml version="1.0" encoding="UTF-8"?>


    

PluginCheckoutLayoutProcessor.php

namespace VendorItalianFiscalAttributesPluginCheckout;

class LayoutProcessor
{
/**
 * @param MagentoCheckoutBlockCheckoutLayoutProcessor $subject
 * @param array $jsLayout
 * @return array
 */
public function afterProcess(
    MagentoCheckoutBlockCheckoutLayoutProcessor $subject,
    array  $jsLayout
) {
    $configuration = $jsLayout['components']['checkout']['children']['steps']['children']['billing-step']['children']['payment']['children']['payments-list']['children'];
    foreach ($configuration as $paymentGroup => $groupConfig) {
        if (isset($groupConfig['component']) AND $groupConfig['component'] === 'Magento_Checkout/js/view/billing-address') {

            $jsLayout['components']['checkout']['children']['steps']['children']['billing-step']['children']
            ['payment']['children']['payments-list']['children'][$paymentGroup]['children']['form-fields']['children']['customer_type'] = [
                'component' => 'Magento_Ui/js/form/element/abstract',
                'config' => [
                    'customScope' => 'billingAddress.custom_attributes',
                    'template' => 'ui/form/field',
                    'elementTmpl' => 'ui/form/element/input',
                    'options' => [],
                    'id' => 'customer_type'
                ],
                'dataScope' => 'billingAddress.custom_attributes.customer_type',
                'label' => 'Customer Type',
                'provider' => 'checkoutProvider',
                'visible' => true,
                'validation' => [],
                'sortOrder' => 1,
                'id' => 'customer_type'
            ];
        }
    }


    return $jsLayout;
}
}