[instagram-api] How to get an Instagram Access Token

100% working this code

<a id="button" class="instagram-token-button" href="https://api.instagram.com/oauth/authorize/?client_id=CLIENT_ID&redirect_uri=REDIRECT_URL&response_type=code">Click here to get your Instagram Access Token and User ID</a>
<?PHP
  if (isset($_GET['code'])) {

        $code = $_GET['code'];

        $client_id='< YOUR CLIENT ID >';
        $redirect_uri='< YOUR REDIRECT URL >';
        $client_secret='< YOUR CLIENT SECRET >';
        $url='https://api.instagram.com/oauth/access_token';

        $request_fields = array(
            'client_id' => $client_id,
            'client_secret' => $client_secret,
            'grant_type' => 'authorization_code',
            'redirect_uri' => $redirect_uri,
            'code' => $code
        );

        $ch = curl_init();
        curl_setopt($ch, CURLOPT_URL, $url);
        curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
        curl_setopt($ch, CURLOPT_POST, true);
        $request_fields = http_build_query($request_fields);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $request_fields);
        $results = curl_exec($ch); 
        $results = json_decode($results,true);
        $access_token = $results['access_token'];

        echo $access_token;

        exit();
    }

?>