I also started getting the same error. No change in my code, and it was working just fine a few days ago. Now getting 401 Unauthorized with message “Client ID and OAuth token do not match”. Was there an update of some sort lately? (I’m also useing the passport-twitch-new package mentioned above. The linked comment was an older issue and did not give me any clues in how to fix this.
There was an announcement months ago that changes to Helix were coming, with scheduled windows that would temporarily apply the change to give people warning if their apps were broken, before going fully live yesterday.
Most Passport modules on Twitch didn’t bother to update to the announced changed, so stopped working.