A discount percent can be applied to the total value of an invoice using our discounts feature, or if you need to discount a particular line of an invoice you can apply this by adding a negative line item.
Adding a discount percent to the full invoice
The discount feature is toggled on from the Settings > Configure system > Toggle features > Invoicing & expenses menu:
This will add a discount % field to the invoice create form:
When you hit the Save button, the discount will be applied to the total value of the invoice and will appear as a new line item:
Adding a discount to a line item on the invoice
If you have multiple line items on an invoice and would like to discount a specific line amount rather than the full invoice amount, you will need to create a new line on the invoice for the discount.
Make sure to enter the unit price as a negative amount, in this example, I am discounting the second line item by 10%.