Trouble with iOS devices with HA app and Duckdns

OK. I am setting up HA and want it on my iOS devices phone and iPad.

Well last week I setup DuckDNS so I could use the HA with Smartthings hub I have now. Then some how i got the HA App to work on my phone (iPhone Xr and my iPad Mini4 ) however now I cannot for the life of me get it to work on any other iPad int he house… the URL is https://subdomain.duckdns.org:8123

All the other iOS device are stating an SSL error. What am I doing wrong and what do I need to do to fix it