This error was meant to indicate that the giving channel has not been entered properly but right now it also appears if the user_read permission has not been granted in scopes.
In April 2018 two users complained about seeing this notice after a plugin update. The solution is to complete the Setup Wizard again and apply user_read, unless the spelling of the channel is the issue.
The plugin already runs some tests, per page request, while you’re on the administration side and requesting any TwitchPress view. The tests results can be found in the Help tab, while you’re on any of the plugins own views.
Various tests are performed to try different areas of the plugin. Each missing or incorrect value requires a different approach to troubleshooting. So don’t get carried away trying to make the plugin work, without being pointed in the right direction by another guide or by asking me!
The one possible fix that you can try for all scenarios is completing the Setup Wizard again. You will find a button to start that in the Installation section of the Help tab you’ve just been looking at above.