Per Caddy documentation, port 80 is also required, and now I suspect the not serving that port is causing Caddy to fail to issue you a tls certificate.
Try adding a simple text response like this (warning, formatting may not be perfect due to typing on mobile). Also setup a port forward on your router to your caddy host on port 80.
my-domain.com:80 { respond “Buzz off” }
Hopefully this will kick off the tls registration and then get your site on 443 working as well.
The article is misleading by leaving out critical details about the amount of energy actually used in the test.
That said, progress is progress.