EasyPost\Shipment::refund PHP Method

    public function refund($params = null)
    {
        $requestor = new Requestor($this->_apiKey);
        $url = $this->instanceUrl() . '/refund';
        list($response, $apiKey) = $requestor->request('get', $url, $params);
        $this->refreshFrom($response, $apiKey, true);
        return $this;
    }