if you are able to run a public web server, then certificate issuance via certbot http challenge works pretty well. the web server can serve a really simple static page with little to nothing on it - but of course its another potential vector into your network.

if your public domain DNS makes use of a supported dns provider or you run your own publically accessible dns server, then dns certbot challenges are great and more flexible than http.

others may suggest neat work arounds for the http challenge issue, but if you have access to a supported dns service I would look at that option. certbot has helpers for quite a few public services as well as support for self hosted dns servers. I run my own public dns servers, so thats the option I chose and use certbot hooks, cron and bash scripts to rsync the updated carts to the propr hosts for the various services I run privately and publicly.

if you are using http cert retrieval, certbot needs a place put the temp. token to authenticate your contrrol of the domain your are creating a certificate for. usually that will be the same webserver you want to serve the certificate from.

if you are not running an actual weberver on port 80 that certbot can insert a token for, certbot cannot complete.

this is, of course, in addition to other possible issues such as ISP port blocking - but without a web server listening on TCP/80, you will have to use other authorization methods (like DNS) to generate a cert.

are you actually running a web server on that host? iirc, certbot will place a temporary token to be served by your web server (Apache, etc.) to show that you actually control the domain you are requesting a cert for.

I switched to DNS based retrieval as soon as let’s encrypt offered it, so its been years since I retrieved certs via http.