HTTPS will only work if you have set up a certificate in your
configuration.yaml under the
http setting. If HTTP works you can just use that. This is based on the assumption that there was not a typo in HTTP/HTTPS
… “http://my-dns-server.duckdns.org:8123” …
… “https://my-dns-server.duckdns.org” …
You shouldn’t be able to access Home Assistant with
“https://my-dns-server.duckdns.org” as the service is listening on
8123 by default, not
80, so that is completely normal.
Please note, if you are using HTTP, all communications to and from Home Assistant will be visible in plain text; meaning someone may be able to exploit your internal network and ruin your day.
There is no need to assume the applet worked, as you can click on My Applets, click to edit your applet, then click on “view activity log” to see if it actually was triggered.
Lastly, did you check to see if am message from IFTTT was received on Home Assistant?