For OpenCart 18.104.22.168
This email is triggered and sent to the voucher receiver when the order status is set to one of the complete order status mentioned in the settings.
Or when the order is updated to complete order status from admin order > Add history
Note: When you go to Admin : Sales > Gift Vouchers > Gift Vouchers, and if you use the email send button here, it will send the default opencart email. Becuase this function uses a seperate individual code to send email and not using events, the extension's customer voucher email will not work here. This will be fixed in our next release of this extension.