public function formPage($action = NULL, $id = NULL) {
    $plugin = $this->customerPagesManager->createInstance($this->customerPagesPlugin, ['action' => $action, 'id' => $id]);
    $form_state = new FormState();
    $form = $this->formBuilder->buildForm($plugin, $form_state);
    $form['#attached']['library'][] = 'core/jquery.form';
    $form['#attached']['library'][] = 'core/drupal.ajax';
    $form['#attached']['library'][] = 'acm_customer/single_page_app';
    $form['#attached']['drupalSettings']['acm_customer'] = [
      'customerPagesPath' => Url::fromRoute('acm_customer.view_page')->toString(),
      'ajaxCustomerPagesPath' => Url::fromRoute('acm_customer.ajax_view_page')->toString(),
    ];
    return $form;
  }