Whats the body message?
The HTTP code is half the information
This is a scope which is added to the URL that users click on to provide permission for your CleintID to read/write data on the users behalf.
Scopes are touched on here Twitch Access Token Scopes | Twitch Developers
And how to construct the URL to auth is here https://dev.twitch.tv/docs/authentication/getting-tokens-oauth#authorization-code-grant-flow