To use the "Following Channels" Feature you need the "user:read:follows" scope.
With this Link you don't have to care about scopes and just get started: https://twitchtokengenerator.com/quick/DvKMUdT92X
After the authentication process copy the Client-Id and the Access Token(Bearer) into the Input fields.
This means that you have specified an incorrect OAuth token, or that this OAuth token was not created in conjunction with the specified client ID.
This error means that you did not specify the required scope to query your followed channels.
This is intentional, a search parameter must be specified first. (This might change in the future)