I am experiencing an issue with FCM (Firebase Cloud Messaging) notifications. While I can successfully send notifications through the FCM console to my iOS device, it does not work when sending notifications from a PHP service. My goal is to be able to send notifications to my app using FCM. I have already implemented web services in PHP for this purpose, which consists of 4 services:

1. group_create.php
2. device_add.php
3. device_remove.php
4. send_comments.php

After creating a group, I was able to obtain a notification key and register a registration ID with FCM. However, when I call the "send_comments.php" service with the notification key, it returns JSON data with {"success":1,"failure":0}, but I do not receive any notification on my iOS device. I have double-checked that all methods are properly implemented. The FCM console works fine, but the PHP service does not. Does anyone know what could be causing this issue? I have attached all 4 PHP files below. Any help would be greatly appreciated.

group_create.php

<?php 
$url = 'https://android.googleapis.com/gcm/notification';

$notification_key_name = $_REQUEST['notification_key_name'];
$regid = $_REQUEST['regid'];
    $fields = array(
       "operation"=>"create",
       "notification_key_name"=>$notification_key_name,
       "registration_ids"=> array($regid)
);
$fields = json_encode( $fields );

$headers = array (
        "Authorization:key=A************************",
        "Content-Type:application/json",
        "project_id:78508******"
);

$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_POSTFIELDS, $fields );

$result = curl_exec ( $ch );

//echo $result;
$res_notification_key = json_decode($result,true);

 if(array_key_exists('notification_key', $res_notification_key)){

$notification_key = $res_notification_key['notification_key'];

 echo $notification_key;

}

else{

echo $result;

}
curl_close ( $ch );
?>

device_add.php

<?php

$senderId = "785********";
$notification_key_name= $_REQUEST['notification_key_name'];
$reg_id = $_REQUEST['regid'];
$notification_key = $_REQUEST['not_key'];
$apiKey = 

$url = 'https://android.googleapis.com/gcm/notification';

  $headers = array (
        "Accept:application/json",
        "Authorization:key=A******************",
        "Content-Type:application/json",
        "project_id:78508*****"
);


 $fields = array(
       "operation"=>"add",
       "notification_key_name"=> $notification_key_name,
       "registration_ids"=> array($reg_id),
       "notification_key"=>$notification_key
);
$fields = json_encode( $fields );

 $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_POSTFIELDS, $fields );


$result = curl_exec ( $ch );

echo $result;
$res_notification_key = json_decode($result,true);

if(array_key_exists('notification_key', $res_notification_key)){


$notification_key = $res_notification_key['notification_key'];

 echo $notification_key;

}

else{

echo $result;

}
curl_close ( $ch );
?>

device_remove.php

<?php

$senderId = "78508*****";
$notification_key_name= $_REQUEST['notification_key_name'];
$reg_id = $_REQUEST['regid'];
$notification_key = $_REQUEST['not_key'];
$apiKey = 

$url = 'https://android.googleapis.com/gcm/notification';

  $headers = array (
        "Accept:application/json",
        "Authorization:key=A***********",
        "Content-Type:application/json",
        "project_id:78508*****"
);


 $fields = array(
       "operation"=>"remove",
       "notification_key_name"=> $notification_key_name,
       "registration_ids"=> array($reg_id),
       "notification_key"=>$notification_key
);
$fields = json_encode( $fields );

 $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_POSTFIELDS, $fields );


$result = curl_exec ( $ch );

echo $result;
$res_notification_key = json_decode($result,true);



if(array_key_exists('notification_key', $res_notification_key)){


$notification_key = $res_notification_key['notification_key'];

 echo $notification_key;

}

else{

echo $result;

}
curl_close ( $ch );
?>

send_comments.php

<?php

$senderId = "78508*****";
$notification_key = $_REQUEST['not_key'];

$url = 'https://fcm.googleapis.com/fcm/send';

  $headers = array (
        "Authorization:key=A*****************",
        "Content-Type:application/json",


);

$msg = array("hello"=>"This is a Firebase Cloud Messaging Device Group Message!");

$msg_dict = json_encode($msg);

 //echo $msg_dict;

 $fields = array(
       "to"=>$notification_key,
       "data"=>array(
            "message" => "hell",

    ),
);
$fields = json_encode( $fields );

 $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_POSTFIELDS, $fields );

$result = curl_exec ( $ch );

echo $result;
$res_notification_key = json_decode($result,true);

curl_close ( $ch );
?>