code: protected function getWsdlIdFor($messageName)
      {
          $msgAndVer = $this->getMessagesAndVersions();
  
          if (isset($msgAndVer[$messageName]) && isset($msgAndVer[$messageName]['wsdl'])) {
              return $msgAndVer[$messageName]['wsdl'];
          }
  
          return null;
      }
docs: Get the WSDL ID for the given message
  
  @param $messageName
  @return string|null