url preview 500 internal server error Missing access token

I set up my own homeserver using the official docker image from matrixdotorg. I tried enabling url previews because they were not working before.

Now when in Element it keeps telling me

Which is frustrating. I played around plenty with my nginx reverse proxy and the homserver.yaml. Even checked if I have the optional depenencies installed. Since this is the official docker image - of course I have them installed.

Someone told me Element can make its own url previews. Doesn't do that for me.

What is going on here? Must be a pretty common problem if it happens on the official docker image. But I got a feeling that I am just stupid. I am not an IT guy, so I have brute-forced myself to setting all of this up.