IOS on mobile devices does not allow pages to open when certificate is invalid.
options: set up a dns server with correct name.
Many routers can do this by default, so i suggest to give tour local network the dns name, and create a dhcp reservation for 192.168.1.45 and name it mvanimpe
In that way, duckdns.org will resolve locally, and mvanimpe will point to 192.168.1.45 
have a look at → HTTPS inside LAN | New Version of HA iOS App - #19 by aceindy
Another solution will be to setup nginx-proxy on ha
Many people seem to do that, but I do not have experience with that :- 