Send FCM Notif via PHP

<?php
function sendFCM($message, $receivers, $api_key){
    $fields = array(
        'registration_ids' => is_array($receivers) ? $receivers : [$receivers],
        'data' => $message,
    );
    $headers = array('Authorization:key='.$api_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);
    return $result;
}