public function createPackage()
    {
        if (!$this->getID()) {
            throw new MissingTrackingParameterException('transaction id is missing');
        }

        return array(
            't' => 'transaction',
            'ti' => $this->getID(),
            'ta' => $this->getAffiliation(),
            'tr' => $this->getRevenue(),
            'ts' => $this->getShipping(),
            'tt' => $this->getTax(),
            'cu' => $this->getCurrency()
        );
    }