Q:

Google GCM server returns Unauthorized Error 401

I am using GCM services to push information from server. If I use browser key it shows the sucess mesaage as : {"multicast_id":4849013215736515938,"success":1,"failure":0,"canonical_ids":0,"results":[{"message_id":"0:1348742583011905%2adac3a0f9fd7ecd"}]}
but i did not get any notifications on device. 
And if I use server key it shows Unauthorized Error 401. My code is shown below:
$apiKey = "xxxxx";
$registrationIDs = array("xxxxxxxx");
$message = "testing Process";
$url = 'https://android.googleapis.com/gcm/send';
$fields = array(
        'registration_ids'  => $registrationIDs,
        'data'              => array("message"=>$message),
        );
$headers = array( 
        'Authorization: key=' . $apiKey,
        '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, 0); 
curl_setopt( $ch, CURLOPT_POSTFIELDS, json_encode($fields) );

$result = curl_exec($ch);
if(curl_errno($ch)){ echo 'Curl error: ' . curl_error($ch); }
curl_close($ch);
echo $result;

Please help me for this issue. Thanks in advance.

A:

Did you whitelist the IP of your server? This is not necessary by default for the browser key, but it is for the server key.
You can check it here:
https://code.google.com/apis/console/#project:[YOUR PROJECT NUMBER]:access

A:

Another answer already suggested whitelisting the IP address, which seems kind of obvious. What fixed it for me was whitelisting my IPv6 address. That was the key! I hope this helps someone else.

A:

I tried everything in this thread, and still no luck. 
So I checked enabled APIs (APIs and Auth -> APIs, Enabled APIs), and realised that I had enabled Google Cloud Messaging for Chrome not Google Cloud Messaging for Android. As soon as I enabled the latter, it worked immediately.
Double check you have the right API enabled!

