I am trying to use this link as a way to local test like you suggessted and it keeps returning a 404 not found.
https://api.twitch.tv/helix/users/Lilrex2015?client_id=x5xnhiu9ax5dn8gkpe08cq3kzffnlf
https://dev.twitch.tv/docs/api/webhooks-reference/#topic-user-changed <-- this is where i got it from.