@markcarey did you get anywhere with this? Hitting the exact same problem
Error 500 Uploading img to your forum
Just FYI, I see an error 500 to https://community.nodebb.org/api/post/upload while trying to upload an image here in this forum.
This does not happen to us in our forum, but we use imgur plugin so I guess that's the reason.
This forum uses the imgur plugin and seems like the imgur upload url is returning 404