Add to Cart link, with product options

[Adilon]

Hello there! I have this link that adds my products to the shopping cart

 

echo '<a href="' . tep_href_link(basename($PHP_SELF), tep_get_all_get_params(array('action')) . 'action=buy_now&products_id=' . $product_info['products_id']) . '">' . "Añadir a la cesta" . '</a>'

 

but the problem is that my product has a listbox with attributes, so when I'm looking at the product at product_info.php, this link doesn't work, what can it be?

 

thanks everyone!