Login php sul mio sito web

First you get a token for the broadcaster, like you did for logging a user in.

Then you make a call to the subscribers API the same way you are already making calls to the users API

you take

        $curl = curl_init('https://api.twitch.tv/helix/user');
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($curl, CURLOPT_HTTPHEADER, array(
            'Client-ID: ' . $client_id,
            'Authorization: Bearer ' . $result['access_token']
        ));
        curl_setopt($curl, CURLOPT_TIMEOUT, 1000);

        $user = curl_exec($curl);
        $i    = curl_getinfo($curl);
        curl_close($curl);

and substitute the variables

        $curl = curl_init('https://api.twitch.tv/helix/subscriptions?broadcaster_id=' . $broadcaster_id . '&user_id' . $user_id);
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($curl, CURLOPT_HTTPHEADER, array(
            'Client-ID: ' . $client_id,
            'Authorization: Bearer ' . $broadcasters_token
        ));
        curl_setopt($curl, CURLOPT_TIMEOUT, 1000);

        $subdata = curl_exec($curl);
        $i    = curl_getinfo($curl);
        curl_close($curl);