function send_notification($tokens, $message) {

    $url = 'https://fcm.googleapis.com/fcm/send';

if ($message) {

$fields = array (

'notification' => array ('body' => $message['body'], 'title' => $message['title'])

);

}

if(is_array($tokens)) {

$fields['registration_ids'] = $tokens;

} else {

$fields['to'] = $tokens;

}

    $fields['priority'] = "high";

    $FCM_SERVER_KEY = ""; 

    $headers = array(

        'Authorization:key =' . $FCM_SERVER_KEY,

        'Content-Type: application/json'

    );

    $ch = curl_init();

    curl_setopt($ch, CURLOPT_URL, $url);

    curl_setopt($ch, CURLOPT_POST, true);

    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);  

    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);

    curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));

    $result = curl_exec($ch);           

    if ($result === FALSE) {

       die('Curl failed: ' . curl_error($ch));

    }

    curl_close($ch);

    return $result;

}

$tokens = "사용자토큰키";

$message = array(

"title"   => "알림제목", 

"body" => "알림내용", 

);

send_notification($tokens, $message);