How to add a document to a resource group

$fields = array(
  'pagetitle' => $title,
  'template' => $templateId,
  'alias' => $pageAlias,
  'published' => $published,
  'parent' => $parent,
  'hidemenu' => 1,
};
 
/* create and save new resource */
$response = $this->modx->runProcessor('resource/create', $fields);
$object = $response->getObject(); 
    $resourceId = $object['id']; 

    // Set the newly created document to the proper group
    $groupName = 'MyGroup';
    $object->joinGroup($groupName);  

$object->save();