I have searched and tried pretty much every post regarding this and am completely lost. After days of trying (and realising my ISP wasn’t allowing port forwarding), I’ve managed to get my supervised install of HA (docker install on Synology NAS) working with DuckDNS and nginx HA SSL proxy. Containers are running fine, certs downloaded and working, but whenever I try to connect via my DDNS xxxxxxx.duckdns.org I get the error 400. Log shows :“A request from a reverse proxy was received from 172.30.33.1, but your HTTP integration is not set-up for reverse proxies”. I have added every flavour possible of IP and ranges to the config.yaml file - including 0.0.0.0/0 and can only come to the conclusion that my config file is not being read by HA. Is there only one file (mine is in docker\homeassistant\homeassistant). Burnt too many hours on this by myself - need some help please !!! 
So pushed the new update, and what do you know - working. Not going to question it, just happy I can crack on with my Tesla charging integration now!!!