Helix does not support Client_ID as a parameter, it has to be provided in the Header. Also, you would pass the ID has a login parameter. Read up on REST parameters to understand what Twitch is asking for here to be passed and how. Be sure to read the differences between Helix and v5, they have a few.
illusion% curl -s -H 'Client-ID: ......' -X GET https://api.twitch.tv/helix/users?login=Lilrex2015 | python -mjson.tool
{
"data": [
{
"broadcaster_type": "",
"description": "Host of The Daily Chat, the ONLY & BEST TRUE TALK SHOW HOST ON TWITCH.TV AND BEAM.PRO/LILREX2015",
"display_name": "Lilrex2015",
"id": "57204065",
"login": "lilrex2015",
"offline_image_url": "https://static-cdn.jtvnw.net/jtv_user_pictures/lilrex2015-channel_offline_image-df75701d8d060ee3-1920x1080.jpeg",
"profile_image_url": "https://static-cdn.jtvnw.net/jtv_user_pictures/lilrex2015-profile_image-5ee09c6d4cd5a201-300x300.png",
"type": "",
"view_count": 21517
}
]
}