Android

Build an object to handle the postMessage call:

class SmartzerPostMessageHandler {
  @JavascriptInterface
  public boolean postMessage(final String json) {
    // parse the json and then do some custom action here using the content of json.cta
    return true; // here we return true if we handled the post.
  }
}

Create a webview and attach the MessageHandler:

  WebSettings webSettings = view.getSettings();
  webSettings.setJavaScriptEnabled(true);
  view.addJavascriptInterface(
    new SmartzerPostMessageHandler(), "smrtzrApp"
  );
  view.loadUrl("<your_player_url>");