function send_notification($token, $title, $body)
{
    $SERVER_API_KEY = "AAAAiyOcU6g:APA91bEAzf_3qesFfsIYTD1UzDz6mjUF_Ivgl5fw4KZkBwJ7tpyUv-g0h4H8RdB5_0649YAZgPCNrsoQNfI8QqwyDdhuC93W-6__G3CMV5GQVo8jLn8ehHOQ0eSW4N9Kn4gGx5WuCu84";
    $header = [
        'Authorization: Key=' . $SERVER_API_KEY,
        'Content-Type: Application/json'
    ];

    $payload = [
        'registration_ids' => [$token],
        'notification' => [
            'title' => $title,
            'body' => $body
        ]
    ];

    $curl = curl_init();
    curl_setopt_array($curl, array(
        CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
        CURLOPT_URL => "https://fcm.googleapis.com/fcm/send",
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_CUSTOMREQUEST => "POST",
        CURLOPT_POSTFIELDS => json_encode( $payload ),
        CURLOPT_HTTPHEADER => $header
    ));

    $response = curl_exec($curl);
    $err = curl_error($curl);

    curl_close($curl);

    if ($err) {
        return response()->json([
            "code" => 1,
            "message" => "cURL Error #:" . $err
        ]);
    } else {
        return response()->json([
            "code" => 0,
            "message" => trans('message.successful'),
            "response" => $response
        ]);
    }
}



$result = send_notification($this->letter->m_sender->token_fcm, 'Thông báo', 'Đã tiếp nhận yêu cầu gửi thư của bạn');