Duck dns not working

Can some one check this isn't me just being an idiot.

Follow the instruction on Google as best I can tell.

Have gone to duck dns have made and account and sub domain they are pointing to my ip address.

Install the duck dns add on on HA. Put in the token and the domain and changed accept terms to true.

Add on is up and running.

I've added a port forward on my router.

For http for the local IP of the device HA in of from external port 443 to internal port 8123

And yet when I go onto an Internet browser and try

Http://(mysubdomain).duckdns.org/

I'm just getting address not found