Facebook Login For Business - User Denied

We have created a new facebook app, using the product Facebook Login for Business.

The app is currently in Dev/Sandbox mode, our business has been verified and advanced access requested where asked. Everytime we test the oAuth flow, it returns the following in callback url:

error=access_denied&error_code=200&error_description=Permissions+error&error_reason=user_denied#_=_

The user testing is an App Admin, Login url is as below:

https://www.facebook.com/v17.0/dialog/oauth?client_id=xxxxxxxxxxxxxxx&redirect_uri=https://example.com/callback&config_id=xxxxxxxxxxxx&response_type=code

The final screen of the login process, facebook side, seems to indicate that it all went well.

We tested both the SDK FB.login() method and manual Login URL, no dice.

We are a bit at loss on what to try next. Suspect there might be something wrong with Facebook Login for Business as it is quite new.

Currently, the app needs to be in Live mode for "Facebook Login for Business" to work. Otherwise, the callback will always say that the user cancelled the process. In dev mode the dialog says that the app was connected but it does not show up in Business Manager - this changes as soon as you have the app in live mode. You will also see that the process takes longer instead of instantly going to the next steps.