Hi,
I didn't say that you should add the code:
echo '<div id="hikashop_add_wishlist">' .
$this->cart->displayButton(JText::_('ADD_TO_WISHLIST'), 'add', $this->params, $url, $wishlistAjax, '', @$this->row->product_max_per_order, 1, '', false) .
'</div>';
It was just an indication of where to put the code of your iframe.
If you want the iframe to be hidden until you click on the add to wishlist button, you need to add an id in your iframe and add CSS code to hide it by default:
#my_iframe_id{ display: none; }
Then, before the code of the add to wishlist button, you need to prepend to the variable $wishlistAjax some javascript code to display the iframe. Something like that:
$wishlistAjax = 'document.getElementById(\'my_iframe_id\').style.display = \'block\''. $wishlistAjax;