code: protected function getSoapClient($msgName)
      {
          $wsdlId = $this->getWsdlIdFor($msgName);
  
          if (!empty($msgName)) {
              if (!isset($this->soapClients[$wsdlId]) || !($this->soapClients[$wsdlId] instanceof \SoapClient)) {
                  $this->soapClients[$wsdlId] = $this->initSoapClient($wsdlId);
              }
  
              return $this->soapClients[$wsdlId];
          } else {
              return null;
          }
      }
docs: Get the appropriate SoapClient for a given message
  
  (depends on which WSDL the message is defined in)
  
  @param string $msgName
  @return \SoapClient