public function check($invoiceId)
    {
        // Clear the error variable
        $this->error = '';

        /**
         * Check value is string
         * If string return false and set error message on error variable
         */
        if (
        !self::__validateString($invoiceId, 1, 50)
        )
            return false;

        $param = array(
            "id" => $invoiceId,
            "apikey" => $this->apiKey,
            "mobile" => $this->mobile
        );

        return self::__sendCheckRequest('invoice', $param);
    }