code: public function trackByReference($referenceNumber, $requestOption = 'activity')
      {
          $this->referenceNumber = $referenceNumber;
          $this->requestOption = $requestOption;
  
          return $this->getFormattedResponse();
      }
docs: Get package tracking information.
  
  @param string $referenceNumber Reference numbers can be a purchase order number, job number, etc. Reference number can be added when creating a shipment.
  @param string $requestOption
  
  @throws Exception
  
  @return stdClass