When running locally should indicate that you'll need to open the app to the /login at http://localhost:8080/login
I found that the only way to use the app with my own Spotify developer credentials was to explicitly whitelist http://localhost:8080/auth under "Redirect URI" in the Spotify app settings.
Might want to throw the haroku link in the read me https://spotify-rec-app.herokuapp.com/login
When running locally should indicate that you'll need to open the app to the /login at http://localhost:8080/login
I found that the only way to use the app with my own Spotify developer credentials was to explicitly whitelist http://localhost:8080/auth under "Redirect URI" in the Spotify app settings.