Hello from child!

<script>
  function msgToParent() {
    const data = { type: 'webview_message', cmd: 'replace_screen', screen: 'formScreen', params: { spec: "whatsapp/spec/form?object_id=21668" }};
    
    window.parent.postMessage(JSON.stringify(data), '*');
  }

  document.getElementById("btn").addEventListener("click", msgToParent);
</script>

<button id="btn" onclick="msgToParent()">Enviar (Filho)</button>