Fcm 401 error when using HttpsURLConnection in java

Question

I'm trying to test out Firebase Cloud messaging in java and used the following code

String url = "https://fcm.googleapis.com/fcm/send";
URL obj = new URL(url);
HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();

//add reuqest header
con.setRequestMethod("POST");                   
con.setRequestProperty("Authorization", "key="+ "<Server-Key>");
con.setRequestProperty("Content-Type", "application/json");
con.setRequestProperty("Accept", "application/json");
con.setAllowUserInteraction(false);
JSONObject infoJson = new JSONObject();

infoJson.put("title", title);
infoJson.put("body", notificationMsg);   

JSONObject infoJson2 = new JSONObject();

infoJson2.put("userId", userId);                
infoJson2.put("title",title);
infoJson2.put("body", notificationMsg);
infoJson2.put("notificationType",  notificationType);
infoJson2.put("badge", String.valueOf(unreadNotificationCount));


JSONObject json = new JSONObject();
json.put("to",clientDeviceToken.trim());
json.put("priority","high");
json.put("content_available",true);

json.put("notification", infoJson);
json.put("data", infoJson2);

                            
if (json != null) {
 con.setDoInput(true);
 con.setDoOutput(true);
 con.setUseCaches(false);

 //send the json as body of the request
 OutputStreamWriter wr = new OutputStreamWriter(con.getOutputStream());
 wr.write(json.toString());
 wr.flush();


//Connect to the server
con.connect();
 
int status = con.getResponseCode();

if( status == 200 ){
    //SUCCESS message
    BufferedReader reader = new BufferedReader(new 
    InputStreamReader(con.getInputStream()));
    System.out.println("Android Notification Response : " + reader.readLine());
}else if(status == 401){
    //client side error
    System.out.println("Notification Response : TokenId : " + clientDeviceToken + " Error occurred :");
}else if(status == 501){
    //server side error
    System.out.println("Notification Response : [ errorCode=ServerError ] TokenId : " + clientDeviceToken);
}else if( status == 503){
    //server side error
    System.out.println("Notification Response : FCM Service is Unavailable TokenId : " + clientDeviceToken);
}

my server key is correct i tested the same json by using postman and it is working. i searched may website all is saying the above code is true, I investigated the reasons for this, and tried it after regenerating new server key, but the error remains constant.

POST /fcm/send HTTP/1.1
Host: fcm.googleapis.com
token_access: 7d29bdce3f93bc35200aef148c6371f264feff54
Content-Type: application/json
Authorization: key=<Server Key>
Content-Length: 357

{"notification":{"title":"Jebosse","body":"Test"},"content_available":true,
"data":{"badge":"1","notificationType":"BR","title":"Jebosse","body":"test ","userId":141},"to":"ee1jP3k7Twmm0AsBTjRpf-:APA91bFd3_z1EQK4t4gvyOERGVMbv-vrdNTr-Z5qaTtoWpXKhIDlo_42gCWj8A1ZJeAQAP1aKxYBpliKUSG7thbHM6JhdXU7g3ubYDB_7MMasyAKcQs8BMqx-xsHxpCEpLzUj2ca3E1h","priority":"high"}

i'am stuck. can any one help me . ?