Dear K.Pongpan ka,
As MK is using the "Re-Direct" payment method on K-Payment Gateway, this process is not using the SSL in the payment process.
We require SSL for sending result back to your backend via RESPURL only. And this process, we have already closed the SSL3.0 for a while.
So, at present, MK could process payment normally. It means that your system is applied to the TLS1.0, TLS1.1, TLS1.2 already ka.
Best regards,