For you to add the amount deducted from the sales invoice, you can create a dedicated item for this expense then add it to the second line item of your invoice. You have to enter the amount as negative to deduct to the total sales of the invoice.
Here's how to do it:
On your left navigation pane, click on the +New button.
Under the Customers column, select Invoice.
Under Products and Services dropdown, choose the item you created for the expense.
Once done, click Save and Close.
Let me include these articles as your future references in running a report and printing them: