code: protected function processSubscriptionForm(FormInterface $form, Request $request): bool
      {
          if (!$form->isSubmitted() || !$form->isValid()) {
              return false;
          }
          
          $availabilityAlertSubscriptionResponseTransfer = $this->getFactory()
              ->getAvailabilityAlertClient()
              ->subscribe(
                  $this->getSubscriptionFormData($form)
                      ->setLocaleName($this->getLocale())
                      ->setStore(Store::getInstance()->getStoreName())
              );
  
          if ($availabilityAlertSubscriptionResponseTransfer->getIsSuccess()) {
              $request->getSession()
                  ->getFlashBag()
                  ->add('availability-alert-success', 'availibility_alert.feedback.success');
  
              return true;
          }
  
          $error = new FormError($availabilityAlertSubscriptionResponseTransfer->getErrors()[0]->getMessage());
  
          $form->addError($error);
  
          return false;
      }
docs: @param \Symfony\Component\Form\FormInterface $form
  @param \Symfony\Component\HttpFoundation\Request $request
  
  @return bool