send Massive push notification to GCM

Question

I have to send Push Notifications with different messages for large number of devices(More than 10k devices per day).But sometimes its not receiving all of the devices.I set up a function pushNotificationToUsers($heading,$message,$registraionids) to send the push notification and I am not sure about my method is correct ,if i am wrong please correct me.

function  pushNotificationToUsers($heading,$message,$registraionids){
        //array of registration ids in $registraionids         
        $key="xxxxxxxxxxx";
        // Set POST variables
        $url = 'https://android.googleapis.com/gcm/send';
        $fields = array(
                        'registration_ids'  =>,$registraionids,
                        'data'              => array( "message" => $message,"title"=>$heading,"soundname"=>"beep.wav" ),
                        );
        $headers = array(
                            'Authorization: key=' . $key,
                            'Content-Type: application/json'
                        );
        // Open connection
        $ch = curl_init();
        // Set the url, number of POST vars, POST data
        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_POSTFIELDS, json_encode( $fields ) );
        // Execute post
        $result = curl_exec($ch);
        // Close connection
        curl_close($ch);

        }

I'm using php in my serverside