Firestore data Update using Java from my android app

Question

if (coin >= 100) {
  herotimer.getDateTime(new Herotimer.VolleyCallback() {
      @Override
      public void onGetDateTime(String date) {
          try {
              Calendar c = Calendar.getInstance();
              SimpleDateFormat sdf = new SimpleDateFormat("MM/dd/yyyy");
              c.setTime(sdf.parse(date));
              c.add(Calendar.DATE,30);
              SimpleDateFormat sdf1 = new SimpleDateFormat("MM/dd/yyyy");
              String output = sdf1.format(c.getTime());
              DocumentReference documentReference = database.collection("users").document(userID);
              Map<String,Object> user = new HashMap<>();
              user.put("date",output);
              documentReference.set(user).addOnSuccessListener(new OnSuccessListener<Void>() {
                  @Override
                  public void onSuccess(Void unused) {
                      Log.d(TAG, "Successfully Updated"+ userID);
                  }
              });

I want to update the data, but it doesn't show any error and does not even update the data. I am Updating the date that comes as Output in the code.