Duckdns with let's encrypt enabled error

I am getting a certificate error. I get to my HA using https://www.myaddress.duckdns.org:8321 but my browser say connection to this site is not secure " identity of this site www.myaddress.duckdns.org:8321 has not been verified"

this is an issue for what I am trying to do. Any ideas?

Have you tried without the www ? Is your port really 8321 not 8123?
Try https://myaddress.duckdns.org:8321