This is after clicking the “Login with GitHub” button. Using Django-allauth.
Got it to work by changing the callback URL under GitHub > Settings > OAuth App > …
The reason it didn’t work before is because I had …/login/callback/ I.e. the full URL. You want to use at least one parent up and remove the forward slash. The redirect_uri that your site then sends to GitHub login mechnism as a URL parameter is of course the full one. I read this somewhere but lost the link just now.