public function getDisplayText() {
        $text = '';
        switch ($this->state) {
            case self::CHARGEABLE:
                $text = __('Chargeable', 'wcexaap');
                break;
            case self::NON_CHARGEABLE:
                $text = __('Non-Chargeable', 'wcexaap');
                break;
            case self::CLOSED:
                $text = __('Closed', 'wcexaap');
                break;
        }

        return $text;
    }