Error when creating new topic

I am getting this error when trying to create a new topic in the forum. I am able to post but I can’t see the preview while I write.

Yeah, I’ve noticed that too. It’s a discourse issue that I hoped they’d fix soon, but it appears they are not being terribly helpful about it right now, so I guess I’ll look for workarounds.

Okay, I think I fixed it by adding some nginx config cruft.