To add a discount to an invoice:

1. Edit or create an invoice
2. Add a separate line item with a negative amount for the discount
3. The total reflects the reduced amount
4. Save the invoice

There is no separate discount field; a negative line item is how you apply a discount in MyCompanyDesk.

Tip: Clearly label the discount line (e.g. "Early payment discount -5%") so the customer understands the deduction.