Open a <sp-dialog> fly out modal

Photoshop UXP Plugin API
1

Hi,
I can’t open a fly-out modal from the panel menu. What am I doing wrong?
Thank you for your help.
Fred

manifes.json

"entrypoints": [
    {
      "type": "command",
      "id": "openStartInterface",
      "label": "Mouli Master"
    }
  ],

main.js

entrypoints.setup({
  commands: {
    openStartInterface: async () => openStartInterface()
});
const openStartInterface = () => {
  document.querySelector('#startInterface').setAttribute('open');
  showAlert("openStartInterface " + document.querySelector('#startInterface').setAttribute('open'))
}

index.html

  <sp-dialog id="startInterface">
    <sp-heading slot="title" size="XS">SELECT THE CAMPAIGN:</sp-heading>
    <sp-body slot="description">Please, select the campaign.</sp-body>
    <div class="row">  
      <sp-action-button id="select" size="M">Select</sp-action-button>
      <sp-heading size="XS" id="showCampaignNane">Lala</sp-heading>
    </div> 
    <div class="row" style="justify-content: center;">
      <sp-button  id="btnCancel" variant="primary" >Cancel</sp-button>
      <sp-button  id="btnStart" selected>START</sp-button>
    </div> 
  </sp-dialog>