code: public function send()
      {
          $optInValue = \OxidEsales\Eshop\Core\Registry::getConfig()->getRequestParameter('c_oegdproptin');
          if ($this->isOptInValidationRequired() && !$optInValue) {
              \OxidEsales\Eshop\Core\Registry::get(\OxidEsales\Eshop\Core\UtilsView::class)->addErrorToDisplay('OEGDPROPTIN_CONTACT_FORM_ERROR_MESSAGE');
              $this->optInError = true;
              return false;
          }
  
          return parent::send();
      }
docs: Validation and contacts email sending
  
  @return bool