Probably wort a try to reinstall it. If you don’t see anything in the DuckDNS add-on log, then the certificatea have not beem generated and that’s also why you get the error in your config because the certs don’t exist.
I uninstalled it, but now I can’t install it again due to the error of being in an unhealthy environment … I’m going to do the Debian Installation and see if solve this things