Can't access Jellyfin from any device other than the host

[Gigigina]

I didn't realise a reverse proxy was necessary for this, I found a few sites that did mention it in the guide. I guess the ones I saw either didn't explain what they were used for or assumed that it was for a single device.
I'm having issues setting that up but that's an issue unrelated to jellyfin itself so I won't be posting that here