Try:
function file_get_contents_curl($url) {
$ch = curl_init();
curl_setopt($ch, CURLOPT_AUTOREFERER, TRUE);
curl_setopt($ch, CURLOPT_HEADER, 0);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, TRUE);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Client-ID: CLIENT-ID'
));
$data = curl_exec($ch);
curl_close($ch);
return $data;
}
$url = 'https://api.twitch.tv/helix/streams?user_login='.$_GET['name'];
$json_array = json_decode(file_get_contents_curl($url), true);
echo $json_array['data'][0]['viewer_count'];