Twitch API currently defaults to v3
v3 requires username
v5 requires userID
You are advised to use v5 and userID and make sure you are setting a version ID in the headers.
As outlined here:
https://dev.twitch.tv/docs/v5/guides/using-the-twitch-api
For example:
curl -H 'Accept: application/vnd.twitchtv.v5+json' \
-H 'Client-ID: uo6dggojyb8d6soh92zknwmi5ej1q2' \
-X GET https://api.twitch.tv/kraken/users?login=dallas,dallasnchains
Note the Accept header.
If you don’t specify a version, you’ll break when Twitch Changes the default API version