FCM Send

<?php
/*
Parameter Example
    $data = array('post_id'=>'12345','post_title'=>'A Blog post');
    $target = 'single tocken id or topic name';
    or
    $target = array('token1','token2','...'); // up to 1000 in one request
*/
public function sendMessage($data,$target){
//FCM api URL
$url = 'https://fcm.googleapis.com/fcm/send';
//api_key available in Firebase Console -> Project Settings -> CLOUD MESSAGING -> Server key
$server_key = 'PASTE_YOUR_SERVER_KEY_HERE';

$fields = array();
$fields['data'] = $data;
if(is_array($token)){
    $fields['registration_ids'] = $target;
}else{
    $fields['to'] = $target;
}
//header with content_type api key
$headers = array(
    'Content-Type:application/json',
  'Authorization:key='.$server_key
);

$ch = curl_init();
curl_setopt($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, false);
curl_setopt($ch, CURLOPT_POSTFIELDS, json_encode($fields));
$result = curl_exec($ch);
if ($result === FALSE) {
    die('FCM Send Error: ' . curl_error($ch));
}
curl_close($ch);
return $result;
}