Simple Invoice supports discounts on individual items as well as on the total invoice amount. To add a discount to a specific item, use the discount column. Only fixed amount discounts are available; percentage discounts are not supported for individual items.
To apply a discount to the entire invoice total, use the Discount button.
You can configure discounts in the Configuration settings. For example, to add a 10% discount to the invoice, adjust the settings as shown below:
The discount will appear in the invoice summary as follows: