OAuth2 redirects to Dropbox.com instead of my redirect URI

Thanks, that's helpful. It looks like your jistix-staging.com/oauth2/dropbox page is itself redirecting back to www.dropbox.com for some reason.

It goes by fast in the log in your video, but here's the relevant portion:

The authorize_submit page is the "Allow" action on the Dropbox app authorization page, which returns a 302 redirect to your redirect URL, giving it the authorization code. Your /dropbox?code=... then itself also returns a 302 redirect back to www.dropbox.com for some reason though. You'll need to debug the code for that route on your web app to see why it's doing that.