error on last step of checkout

-- url of the page with the problem -- : votandsp.com/yoo_nano3_demo_package_j31/index.php/telepathy use add to cart button on right hand side
-- HikaShop version -- : latest
-- Joomla version -- : latest
-- PHP version -- : x.x.x
-- Browser(s) name and version -- : chrome
-- Error-message(debug-mod must be tuned on) -- : Error_message

On last step of checkout, I get the following error :
Fatal error: Call to undefined function ImageCreateFromPNG() in /home/......./public_html/............/administrator/components/com_hikashop/helpers/image.php on line 762

Hi,

The function ImageCreateFromPNG() comes from the PHP GD Library.
www.php.net/manual/en/function.imagecreatefrompng.php

Please check that this library is right enabled in your web server. Otherwise, all the thumbnails and image generation features won't be able to work.

Regards,

PS: "latest" is not a version number. The current "stable" package is 2.2.1 but the current download package is 2.2.2