Send android notification messages to Firebase Messaging

<?php
// Vladimir Zhelnov - neatek.pw - Web/iOS dev
// PushServer for Radiovera.ru

// Your Message
$data = [
    "to" => "/topics/push", // here is Topic (create in AndroidApp, or device token)
// customizated notification message on override onMessageReceived Android App
    "data" => [
        "message" => "Привет мир",
        "title" => "РАДИО ВЕРА"
    ],
// here is default notification without customization
/*    "notification" => [
      "body" => "Привет мир",
      "title" => "РАДИО ВЕРА",
      "icon" => "myicon",
      "sound" => "default"
    ]*/
];

// Process send that notification to users
$data_string = json_encode( $data );
$ch = curl_init('https://fcm.googleapis.com/fcm/send');
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER,
    [
        'Content-Type: application/json',
        'Content-Length: ' . strlen($data_string),
        'Authorization: key=HERE_IS_TOKEN_OF_FIREBASE_MESSAGING'
    ]
);
$result = curl_exec($ch);
var_dump($result);