src/Tracking.php
public function trackByReference($referenceNumber, $requestOption = 'activity')
    {
        $this->referenceNumber = $referenceNumber;
        $this->requestOption = $requestOption;

        return $this->getFormattedResponse();
    }
public function trackByReference($referenceNumber, $requestOption = 'activity')
    {
        $this->referenceNumber = $referenceNumber;
        $this->requestOption = $requestOption;

        return $this->getFormattedResponse();
    }
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