This section comes into the picture when the gift card payment is done through the offline mode. Therefore, for such cases, the admin has to generate the invoice.

In order to do so:
From the admin panel: Click on 

                                                                                      Sales > Orders

Once we click on the “Orders” button admin would be redirected to the orders page.

Here, the admin sees the grid of order that is available.
For the order whose invoice needs to be generated, admin goes to that particular order and click on “View” button

Once admin click the “View” button, an admin would be redirected to that particular order.

In order to generate the invoice for that particular order, we click the “Invoice” button.

Here, we update the number of items for which we need to generate the invoice. Once admin does so, he clicks on the “Submit button”.

Now, we will be getting a success message “The invoice has been generated”. And we could clearly see the status has been changed to “Completed”.
Note: The credit memo will not be shown for the gift card product purchase.