When i try to send Push notification from PHP i get Unauthorized Error 401 . why?

Question

Given below is code which i am using .

<?php


// API access key from Google API's Console


define( 'API_ACCESS_KEY', 'AIzaSyAyX-***********SKFpTh_Bc' );


$registrationIds =  array('eZnvyFhSS******************************3Dcnpm2QQZFN3GD1Q3L6LWbmeWzajv2

povldIaOMU-ji7CMuous2hPS1n7Q7WaQCe1yD4QUQF50U5uW3U1dQ_8yJakol_QP');
// prep the bundle


$msg = array
(

    'message'   => 'here is a message. message',

);

$fields = array
(

    'registration_ids'  => $registrationIds,

    'data'          => $msg
);

$headers = array
(
    'Authorization: key=' . API_ACCESS_KEY,

    'Content-Type: application/json'
);


$ch = curl_init();

curl_setopt( $ch,CURLOPT_URL, 'https://android.googleapis.com/gcm/send' );

curl_setopt( $ch,CURLOPT_POST, true );

curl_setopt( $ch,CURLOPT_HTTPHEADER, $headers );

curl_setopt( $ch,CURLOPT_RETURNTRANSFER, true );

curl_setopt( $ch,CURLOPT_SSL_VERIFYPEER, false );

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


$result = curl_exec($ch );

curl_close( $ch );


echo $result;