Problem with confirming subscription pubsubhubbub

The first code:

if(isset($_GET["hub_challenge"])) {
    echo $_GET["hub_challenge"];

    }
    else {

    }
    $feeded = $_POST['feed']; 
    $ch = curl_init("http://pubsubhubbub.appspot.com");
    curl_setopt($ch, CURLOPT_POST, TRUE);
    curl_setopt($ch,CURLOPT_POSTFIELDS,"hub.mode=subscribe&hub.verify=async&hub.callback=http://rssreaderbg.net/pubsubbub/example/index.php?url=$feeded&hub.topic=$feeded");
    curl_exec($ch);

The callback code:

file_put_contents("logmeme.txt",$HTTP_RAW_POST_DATA,FILE_APPEND);

https://pubsubhubbub.appspot.com/topic-details?hub.url=http%3A%2F%2Frssreaderbg.net%2Fblog%2F%3Ffeed%3Drss2

https://pubsubhubbub.appspot.com/subscription-details?hub.callback=http%3A%2F%2Frssreaderbg.net开发者_开发知识库%2Fpubsubbub%2Fexample%2Findex.php&hub.topic=http%3A%2F%2Frssreaderbg.net%2Fblog%2F%3Ffeed%3Drss2&hub.secret=

It can't reach the callback url or ?

Try explicitly setting the header to 2xx before echoing the challenge.

header('HTTP/1.1 204 "No Content"', true, 204);