Checkout pop-out to continue shopping

-- url of the page with the problem -- : www.raburt.co.nz/browse/balls-and-hearts/product/880-bsst
-- HikaShop version -- : 4.4.1
-- Joomla version -- : 3.9.25
-- PHP version -- : 7.4.15
-- Browser(s) name and version -- : Firefox

Hello, with reference to www.hikashop.com/forum/checkout/900465-c...button-in-popup.html , I cannot find or install the Add to Cart Notification plugin. If I search my plugins for 'add', I only see the Hikashop Address Plugin, nothing else either installed or inactivated. I have also Downloaded the Business version of Hikashop and re-installed the latest version but this made no difference.