First, you can get rid of 'Accept': 'application/vnd.twitchtv.v5+json' as v5 is part of the old API and not part of the new API (Helix) so doesn’t do anything.
Secondly, I don’t know the the structure of your users array and user objects, but you’re mapping over a users array, and using the variable affiliate for each user in that array, but you’re never actually using that anywhere. The places where you’re wanting to use a Twitch ID you’ve used users.twitchUserId, which if users is an array will mean that’s undefined.
I believe what you intended was to use affiliate.twitchUserId which would be the ID of each user in that array.