Select the next available item line then for a service invoice, enter some details and press F3. For a product invoice, press the arrow and double click a special product.
Select the Make negative checkbox.
For the Unit Price, enter the amount as a positive value.
Complete the item line details, then press OK.
Enter any other items as required.
Press Save then Close.
NOTE:
The negative items mustn't exceed the total value of the positive items on the invoice. Under the VAT Cash Accounting scheme, the total value of negative items per tax code must not exceed the tax code's total value.