public function create($recurringApplicationChargeId, UsageCharge $usageCharge)
    {
        $data = $usageCharge->exportData();
        $endpoint = '/admin/recurring_application_charges/'.$recurringApplicationChargeId.'/usage_charges.json';
        $response = $this->request(
            $endpoint, 'POST', array(
            'usage_charge' => $data
            )
        );
        $usageCharge->setData($response['usage_charge']);
    }