public function __toString() {
        $debugmsg = is_callable($this->debugmsg) ? '' : $this->debugmsg;
        $message = is_callable($this->message) ? '' : $this->message;
        $adminmsg = is_callable($this->adminmsg) ? '' : $this->adminmsg;

        $s = '(Code: ' . $this->errorcode . ') (Name: ' . $this->errorname . ') [DebugMessage]: ' . $debugmsg;
        $s .= ' [UserMessage]: ' . $message;
        if (!empty($adminmsg)) {
            $s .= ' [AdminMessage]: ' . $adminmsg;
        }
        if (!empty($this->transactionId)) {
            $s .= ' [LINE Pay transaction ID]: ' . $this->transactionId;
        }
        if (!empty($this->orderId)) {
            $s .= ' [LINE Pay order ID]: ' . $this->orderId;
        }

        return $s;
    }