Testing Notifications

Could you activate the debug mode of your payment plugin and try again. Then, via FTP, retrieve the payment log file (the location is indicated in the option "Payment log file", under the tab files of the configuration) and upload it in your next post ?

Yes. Send us a back end access and a FTP access to your website and we'll look at all that.

I've changed a bit the code of the email and I added the two lines below so that the customer information is loaded, so that the system can pick up the email address automatically. That seems to have fixed the problem.
$userCl = hikashop::get('class.user');
$data->customer = $userCl->get($data->order_user_id);