graph api notifications returns empty data - php

Question

im building a facebook app and i want to notify the user
https://developers.facebook.com/docs/games/notifications
im using facebook php sdk
what i do:
user auths the app and accepts permission
i get the accesstoken like:
$facebook->getAccessToken()
and then i generate a long-time token like:
public function generateLongTimeToken($token){
$long_time_token_req_body = array(
"grant_type"=>"fb_exchange_token",
"client_id"=>$this->facebookOptions["appId"],
"client_secret"=>$this->facebookOptions["secret"],
"fb_exchange_token"=>$token
);
$query = http_build_query($long_time_token_req_body);
$lttreq = file_get_contents("https://graph.facebook.com/oauth/access_token?".$query);
$lttresp = parse_str($lttreq, $output);
if ( array_key_exists("access_token", $output)){
$this->logger->info("Facebook-app: Successfuly generated long_time_token");
return $output["access_token"];
}else {
$this->logger->err("Facebook-app: generating oauth long_time_token failed \n".$lttreq);
return false;
}
}
some later i use this token for background processes to post on the users wall and them all work fine
now i also want to notificate the user like that :
public function notifyUser($message,$facebookClientId,$token){
$appsecret_proof= hash_hmac('sha256', $token, $this->facebookOptions["secret"]);
$req_body = array(
"access_token"=>$token,
"appsecret_proof"=>$appsecret_proof,
"href"=>"/index",
"template"=>$message,
"ref"=>"post"
);
$query = http_build_query($req_body);
$url = "https://graph.facebook.com/".$facebookClientId."/notifications?".$query;
$lttreq = file_get_contents($url);
return $lttreq;
}
but when i try to notify the user i always get empty data back
when i open the url in browser with all parameters facebook returns the same
{
data: [ ]
}
so i have no idea whats going on,when i look on SO i only find about people posting to sites but i want to notify the user itself
thanks for any help

Answer 1

First, from the Facebook docs:
Currently, only apps on Facebook.com can use App Notifications.
Notifications are only surfaced on the desktop version of
Facebook.com.
Also, an App Token is needed, not a User Token.
Btw, file_get_contents is very bad, use CURL for Facebook. May be another reason why it does not work. A basic example of using CURL with the Facebook API: http://www.devils-heaven.com/extended-page-access-tokens-curl/
Additional Info: I recently wrote a blogpost about App Notifications, it is in german but the small code part may be interesting for you: http://blog.limesoda.com/2014/08/app-notifications-facebook-apps/