Use cURL and specify headers.
With no headers it defaults to v3 and theres no clips endpoints on v3.
Also on most hosts file_get_contents over HTTP is blocked as it’s unsafe.
It looks like it should work with your code, but just don’t use file_get_contents as a rule
However the correct opts is:
$opts = [
"http" => [
"method" => "GET",
"header" => "Client-ID: ".$this->client_id . "\r\n"
"Accept: application/vnd.twitchtv.v5+json\r\n"
]
];