Error logging in using reverse proxy


I’ve just re-installed home assistant as I’ve moved to a new sever, this time using Hyper-V.

All seems to be going well except I’m using a reverse proxy (nginx proxy manager in docker) and have set it up to point to the local address of the VM. It is working and secure, it takes me to the login page, but after entering my details, I get the error below.

All my other proxied hosts work (Plex, ombi etc) but this throws that error after logging in.

Have I missed something?