The error is in your URL
endpoint = "https://api.twitch.tv/helix/users?" + streamer
Should be, if you have a username to lookup
endpoint = "https://api.twitch.tv/helix/users?login=" + streamer
or if you have a username to look up
endpoint = "https://api.twitch.tv/helix/users?id=" + streamer
or if you have a user access token and what the user
endpoint = "https://api.twitch.tv/helix/users"