The grant type is client_credentials it’s literally the word client_credentials. Not sure what you mean by I just don’t understand what client_credentials should be? since the grant_type for The Client Credentials OAuth Flow is client_credentials
POST https://id.twitch.tv/oauth2/token
?client_id=<your client ID>
&client_secret=<your client secret>
&grant_type=client_credentials
Which’ll return JSON blob including an access_token
You then use that access_token in your header that already has the client-id in with your request to helix, as described in the announcment post I linked
So
https://api.twitch.tv/helix/streams?user_login=french_barttv
headers:
client-id: yourClientId
authorization: Bearer yourAccessToken
Where yourAccessToken is from the Client Credentials post