You haven't added any redirect_uri,
that is the url that will receive the code or access-token in OAuth2 flow.
There's NO NEED to add http://localhost:* as by default,
SimpleLogin whitelists localhost (unlike Facebook).
You DO need to add your redirect_uri once your app goes live (i.e. deployed on production).
The redirect_uri needs to be HTTPS for security reason.
Start by adding your first redirect_uri here 👇
{% endif %}
{% for redirect_uri in client.redirect_uris %}