public function setTrial($enable = false, $days = null, $hold_setup_fee = false)
    {
        $this->data->trial = new stdClass;
        $this->data->trial->enabled = (boolean) $enable;
        $this->data->trial->days = $days;
        $this->data->trial->hold_setup_fee = (boolean) $hold_setup_fee;

        return $this;
    }