code: protected function getActiveVersionFor($messageName)
      {
          $msgAndVer = $this->getMessagesAndVersions();
  
          $found = null;
  
          if (isset($msgAndVer[$messageName]) && isset($msgAndVer[$messageName]['version'])) {
              $found = $msgAndVer[$messageName]['version'];
          }
  
          return $found;
      }
docs: Get the version number active in the WSDL for the given message
  
  @param $messageName
  @return float|string|null