Update sub category with api webservices

[Sevarf2]

Hello,

I need tp update the subcategories using the webservice api.

I'm able to update the main categories using this code

$mycategories = array(1,2,3,4,5);
unset($item->associations->categories); 
$categories = $item->associations->addChild('categories'); 
foreach( $mycategories as $cat ){
  $category = $categories->addChild('category');
  	$category->addChild('id', $cat);
  }
}

and I tried to apply the same logic with sub categories, adding another associations item to the category and again categories and category but it's not doing anything.

$category->addChild('associations')->addChild('categories')->addChild('category');

Thanks

[Sevarf2]

my bad, sub categories work as main categories...