PayPal\Api\Item::addSupplementaryData PHP Method

    public function addSupplementaryData($nameValuePair)
    {
        if (!$this->getSupplementaryData()) {
            return $this->setSupplementaryData(array($nameValuePair));
        } else {
            return $this->setSupplementaryData(array_merge($this->getSupplementaryData(), array($nameValuePair)));
        }
    }