public function getManifest($manifest_id, $rel = '', array $options = [])
    {
        if (!empty($rel) && ($rel !== 'details')) {
            $message = sprintf(
                'Unsupported "rel" value: "%s". Supported "rel" value are "details" or null.',
                $rel
            );
            throw new \InvalidArgumentException($message);
        }

        $endpoint = sprintf(
            'rs/%s/%s/manifest/%s/%s',
            $this->config['customer_number'],
            $this->config['customer_number'],
            $manifest_id,
            $rel
        );
        $response = $this->get(
            $endpoint,
            ['Accept' => 'application/vnd.cpc.manifest-v8+xml'],
            $options
        );
        return $response;
    }