It is necessary to get data from remotemessage FCM. When receiving a message, the data is null

I am trying to transfer the data as follows.

public void SendNotifications() {


      String numberAuto = MainAdapter.gosNumber.getText().toString();
      String token =  userFcmToken;

       requestQueue = Volley.newRequestQueue(mActivity);
        Map<String, String> header = new HashMap<String, String>();
        header.put("data", "title");

        JSONObject mainObj = new JSONObject();
        try {
            mainObj.put("to", token);
            mainObj.put("data", header);

            JsonObjectRequest request = new JsonObjectRequest(Request.Method.POST, postUrl, mainObj, new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    System.out.println("FCM" + response);
                }
            }, new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                   Toast.makeText(mContext, "bad", Toast.LENGTH_SHORT).show();
                }
            }) {
                @Override
                public Map<String, String> getHeaders() throws AuthFailureError {
                    Map<String, String> header = new HashMap<>();
                    header.put("content-type", "application/json");
                    header.put("authorization", "key=" + fcmServerKey);
                    return header;
                }
            };

       requestQueue.add(request);
            

        } catch (JSONException e) {
            e.printStackTrace();
        }
}

and get in. I don’t understand how to properly assemble a query with data.

public class FirebaseMessagingServices extends FirebaseMessagingService 

public void onMessageReceived(RemoteMessage remoteMessage) {
        super.onMessageReceived(remoteMessage);

       Map<String, String> header = remoteMessage.getData();
        JSONObject text;
        text = new JSONObject(header);
        Log.d(SCREEN_TOGGLE_TAG, "" + text.toString());
        
}