@Sungjun_Na Yes, I see Netlify’s NS records for that domain.
You can work through the troubleshooting tips here:
https://docs.netlify.com/domains/troubleshooting-tips/
There’s also this support guide:
https://answers.netlify.com/t/support-guide-troubleshooting-ssl-certificate-errors/39865
It might be that you need to wait for Netlify’s assistance though.
Often when they help with these tickets they do so privately, so I’m not sure what the fix tends to be.