Hi @Sangkwun
checked your domain online there are only timeouts (via demo.lomin.ai - Make your website better - DNS, redirects, mixed content, certificates ):
| Domainname | Http-Status | redirect | Sec. | G |
|---|---|---|---|---|
| • http://demo.lomin.ai/ | ||||
| 147.46.238.11 | -14 | 10.023 | T | |
| Timeout - The operation has timed out | ||||
| • https://demo.lomin.ai/ | ||||
| 147.46.238.11 | -14 | 10.030 | T | |
| Timeout - The operation has timed out | ||||
| • http://demo.lomin.ai/.well-known/acme-challenge/check-your-website-dot-server-daten-dot-de | ||||
| 147.46.238.11 | -14 | 10.027 | T | |
| Timeout - The operation has timed out |
So it's impossible to Letsencrypt to check your file. Your site is invisible.