Reverse proxy works EXCEPT on iPhone

I have a weird problem, that to me, makes no logical sense.

I set up Grafana in docker, and configured my reverse proxy in nginx. All seemed to be working perfectly. I could visit grafana at with no problems. Or so I thought… I then tried to load it on my iPhone, both in Safari and Chrome but got the “If you’re seeing this Grafana has failed to load its application files” error. Obviously the reverse proxy is working as I can access it from a computer (macOS using Safari)… but just not on iOS. Any tips?