In your awesome post you mentioned that callback url is required but you don't show what you entered in the screenshots nor the post.
Can you share that?
I can run both the frontend and backend apps but it fails on the call back url which is required. Since you say it doesn't matter, I thought to simply put: http://127.0.0.1:4000/
I go through the screen of allowing email in the popup and then this appears:

Then I tried http://127.0.0.1:3000/ and I got some nice inception happening

I can see the token as a param in that url - but I believe the token should be processed in the backend app not the frontend app. That's why port 4000 should be used....but it's not working.
What did you put as a callback url?