The HTTP Request is never sent since the authentication is causing a 400 Bad Request before that. Authentication works fine when testing using curl. Also tried changing it to Authorization Code with some placeholders to produces a similar request with no success.
Looking at the docs for Twitch are you also remembering to set the Client-Id header in the request? We will handle sending the Authorization header but Twitch seems to have an extra step of needing the client-id to be sent as a header as well on all API requests.