public function render($email_id, $args = null) {
        $endpoint = "render";

        $payload = array(
            "template_id" => $email_id
        );

        if (is_array($args)) {
            $payload = array_merge($args, $payload);
        }

        if ($this->DEBUG) {
            $this->log_message(sprintf(
                "rendering template `%s` with \n%s",
                $email_id,
                print_r($payload, true)
            ));
        }

        return $this->api_request($endpoint, self::HTTP_POST, $payload);
    }