Sorting repository by more than one attribute

I want to sort a repository by more than one attribute. Any ideas of how to achieve this?

What I have so far is this:

public function getLatestPosts()
{
  return $this->postRepository
   ->getList($this->buildSearchCriteriaForLatestPosts())
   ->getItems();
}

private function buildSearchCriteriaForLatestPosts()
{
  $this->prepareSearchCriteriaBuilder();
  $this->searchCriteriaBuilder->setPageSize(1);
  return $this->searchCriteriaBuilder->create();
}

private function prepareSearchCriteriaBuilder()
{

   /** @var MagentoFrameworkApiSortOrder $publishDateOrder */
   $publishDateOrder = $this->sortOrderBuilder
      ->setField(PostInterface::PUBLISH_DATE)
      ->setDirection(SortOrder::SORT_DESC)
      ->create();

   /** @var MagentoFrameworkApiSortOrder $isFeaturedOrder */
   $isFeaturedOrder = $this->sortOrderBuilder
      ->setField('is_featured')
      ->setDirection(SortOrder::SORT_DESC)
      ->create();

   $this->searchCriteriaBuilder->setSortOrders([$publishDateOrder, $isFeaturedOrder]);
}

I dont know why it is not working properly; what I want to achieve is to get the list of Posts sorted by is_featured and created_at in DESC. So even if somehow 2 or more posts are featured, it will display the latest one at the top

Any help will be appreciated!
Thanks