Hi,
It looks like you have an item custom fields which does not exists.
You can edit the email file and replace
if(empty($item->$namekey) && !strlen($item->$namekey)) continue;
By
if(!isset($item->$namekey) || (empty($item->$namekey) && !strlen($item->$namekey))) continue;
And it should fix the notice message.
Please note that it is just a notice ; it's not an error or a really big issue ; it will not break the HikaShop process and in production website, the PHP message should be hidden (but for sure, we do our best to remove all notices).
Regards,