Please check that url. That's the url Letsencrypt checks to validate your domain. There is a nginx.
Read required basics:
PS:
404 Not Found
nginx
I don't think that's the output of your IIS.
PPS: There is a check of your domain, ~~3,5 hours old - https://check-your-website.server-daten.de/?q=ht930.com#url-checks
Same:
http://ht930.com/
148.72.215.11
Server: nginx
Date: Wed, 20 Jan 2021 17:08:07 GMT
Only nginx - answers.