original_string: public function actionNotify(string $transactionId = null)
      {
          $transaction = $this->checkNotify($transactionId);
          if ($transaction === null) {
              return 'Unknown transaction';
          }
  
          Yii::$app->response->format = Response::FORMAT_RAW;
  
          return $transaction->isConfirmed() ? 'OK' : $transaction->getParameter('error');
      }
code: public function actionNotify(string $transactionId = null)
      {
          $transaction = $this->checkNotify($transactionId);
          if ($transaction === null) {
              return 'Unknown transaction';
          }
  
          Yii::$app->response->format = Response::FORMAT_RAW;
  
          return $transaction->isConfirmed() ? 'OK' : $transaction->getParameter('error');
      }
code_tokens: public function actionNotify ( string $ transactionId = null ) { $ transaction = $ this -> checkNotify ( $ transactionId ) ; if ( $ transaction === null ) { return 'Unknown transaction' ; } Yii :: $ app -> response -> format = Response :: FORMAT_RAW ; return $ transaction -> isConfirmed ( ) ? 'OK' : $ transaction -> getParameter ( 'error' ) ; }
docstring: Action handles notifications from payment systems,
  processes them and report success or error for the payment system.
  
  @param string|null $transactionId Parameters is NOT required because some merchants may NOT send it, or send in POST or JSON body.
  The main purpose of these parameters is handling of special routes using UrlManager
  
  @return null|string
  @throws InvalidConfigException
docstring_tokens: Action handles notifications from payment systems processes them and report success or error for the payment system .