Got it working by going to the sample link
GET 'https://id.twitch.tv/oauth2/authorize?response_type=token&client_id=uo6dggojyb8d6soh92zknwmi5ej1q2&redirect_uri=http://localhost&scope=viewing_activity_read
with scope as viewing_activity_read
The OAuth token from this response works. Not sure why adding the scope=viewing_activity_read works but it works for me.