Custom UI

public class ScoreHud extends CustomUIHud {
    @Override
    protected void build(@Nonnull UICommandBuilder ui) {
        ui.append("Hud/Score.ui");
    }
    public void updateScore(int score) {
        UICommandBuilder ui = new UICommandBuilder();
        ui.set("#ScoreText.Text", String.valueOf(score));
        update(false, ui);  // false = incremental update
    }
}

{
  "Identifier": "ScoreHud",
  "Root": {
    "Type": "Panel",
    "Anchor": { "Top": 10, "Right": 10, "Width": 100, "Height": 30 },
    "Children": [
      {
        "Identifier": "ScoreText",
        "Type": "Label",
        "Text": "0",
        "Font": "Default",
        "FontSize": 24,
        "Color": "#FFFFFF"
      }
    ]
  }
}

public class ShopPage extends InteractiveCustomUIPage {
    @Override
    protected void build(@Nonnull UICommandBuilder ui) {
        ui.append("Pages/Shop.ui");
    }
    @Override
    protected void onCallback(String callbackId, String data) {
        if ("buy_item".equals(callbackId)) {
            // Handle purchase
        }
    }
}

// HUD - persistent
ScoreHud hud = new ScoreHud();
player.getHudManager().setCustomHud(playerRef, hud);
hud.show();
// Page - modal
ShopPage page = new ShopPage();
player.getUIManager().show(page);