Add the customer's email address in the invoice

-- HikaShop version -- : 4.5.1 Business
-- Joomla version -- : 3.10.9

Hello,
I need to add the customer's email address in the invoice available in administration.
I have found which view to edit (order/invoice.php), but I don't know how to call the email address.
Thank you for your help.

It's ok I found...

<?php echo @$this->order->customer->user_email; ?>