There are 3 different ways to add a discount to an invoice:
Line item discount - apply a discount to an individual item
Click the number in the "Gross Discount" column of the item that you wish to apply a discount to.
Enter the discount amount and click the tick.
Invoice discount - apply a discount to the entire invoice
Underneath the invoice, use the drop downs next to "Invoice Discount" - choose £ or % depending on whether you want a discount amount or %.
Chose the value or % amount to apply.
Tip: 💡
Applying a flat discount amount (e.g. £10) to the invoice will be spread across the items in proportion to their value.
Promotion discount
If you have created a discount and an item in the invoice matches its rules, the discount will be available to select in the "Promotion Discount" drop down.
Select the discount you wish and it will be applied.
Learn how to Create a promotion discount
Tip: 💡
At the time of writing this article (July 2023), only one Promotion discount can be applied to a discount at a time.