That’s what you get if you open https://twitch-proxy.freecodecamp.rocks/helix/streams?user_login=freecodecamp on your browser, you are not doing something wrong
You can use the static snapshot API data with the listed users (the demo uses it). But if you want to use the twitch API I would suggest you use the real one.
The proxy API might have been misused (by third parties) so it can’t generate a new API key for the proxy. I only looked at the proxy code briefly but didn’t see anything obvious.