Instagram Display API Insufficient Developer Role

What fixed this for me when trying to use this link:

https://api.instagram.com/oauth/authorize
  ?app_id={app-id}
  &redirect_uri={redirect-uri}
  &scope=user_profile,user_media
  &response_type=code

... was being logged in as the accepted Testing User in the same browser session.

I had logged in as that user in an Incognito window, and originally the link was returning that Insufficient Developer Role error when I was trying it in my normal browser window.

Once tried to go to it in the incognito window, it worked just fine.

Let me know if this fixes it for you. Otherwise, I also went to my Developer Settings and did the Individual Verification, although my ID hasn't been approved yet and it still worked.

Go to Roles > Instagram Users and add your Instagram account. Then go to https://www.instagram.com/accounts/manage_access/ to accept the Tester Invite from your app.