Renew Let’s Encrypt certificate automatically

In my https section,
portfolio.kimdonghee.dev doesn’t appear to be served by Netlify

We can’t renew your Let’s Encrypt certificate automatically until the issue is resolved. Check our troubleshooting guide for more information on how to fix the problem, and then renew the certificate.

How can I fix this problem?

There was nothing changed, but when I checked today, there was a sudden error.

You seem to have moved on from using Netlify DNS:

Check this out: