请求未发送到fcm（firebasecloudmessaging）服务器

I want to implement push notification using fcm and I built a server using php which takes request from the android application.Data is coming from app,but server is not sending. Following is the app server code which wantt to request fcm server with "path_to_kinga":

<?php
require "con1.php";
$message=$_POST['Message'];
$title =$_POST['title'];
$path_to_kinga='POST https://fcm.googleapis.com/fcm/send';
$server_key  =
"AAAAJsED6Us:APA91bGelYoGbeB0BdVBwZji0QvXh4pigDjMJRiakWdivEPYHlLF94N _ 
Gj2eIVsXF7VYQVcNOSHC2SQPBdAsgK9BYNbpEFxGASY4L2L6AB8Z_NuM8vXs96QLV6IK416jATQp
TYgiZDvx9NYMXZbsR9rka_2I1N5Jyw";
$sql="select tokens from token_data";
$result=mysqli_query($con,$sql);
$row=mysqli_fetch_row($result);
$key=$row[0];
$headers=array(
'Authorization:key=' .$server_key,
'content-Type:application/json'
);
$fields=array('to'=>$key,'notification'=>array('title'=>$title,
'body'=>$message),'content_available'=>true); 
$payload =json_encode($fields);
$curl_session=curl_init();
curl_setopt($curl_session,CURLOPT_URL,$path_to_kinga);
curl_setopt($curl_session,CURLOPT_POST,true);
curl_setopt($curl_session,CURLOPT_HTTPHEADER,$headers);
curl_setopt($curl_session,CURLOPT_RETURNTRANSFER,true);
curl_setopt($curl_session,CURLOPT_SSL_VERIFYPEER,false);
curl_setopt($curl_session,CURLOPT_IPRESOLVE,CURLOPT_IPRESOLVE_V4);
curl_setopt($curl_session,CURLOPT_POSTFIELDS,$payload);

$result =curl_exec($curl_session);
curl_close($curl_session);
mysqli_close($con);
?php