Order/Order Invoice
From Shopnix Help
What is order invoice ?
Order invoice is the receipt of the order placed by the customer. You can take a printout or email to the customer regarding their order.
Where to get this feature ?
Go to Admin > Orders
then click on the invoice icon (red square in above image) under invoice column. Then a pop will emerge with all the details i.e. order ID, shipping address, number of orders and prices, etc like below image.