private function getExpirationDate($expiryMonth, $expiryYear) {
        $expDate = new DateTime(
            $expiryYear
            . '-'
            . $expiryMonth
            . '-'
            . '01'
            . ' '
            . '00:00:00',
            new DateTimeZone('UTC')
        );

        return $expDate->add(new DateInterval('P1M'))->format('Y-m-d 00:00:00');
    }