You do not need
request.Accept = “application/vnd.twitchtv.v5+json”;
With helix.
I called https://api.twitch.tv/helix/streams?user_login=carlosalbertophelippe
And I got data:
You need to give it 3/5 minutes after starting the stream before it will show up in helix. Due to caching.
You may also consider using webhooks https://dev.twitch.tv/docs/api/webhooks-guide