You can do this by using the special product codes S1, S2 and S3. You can also add negative lines to service invoices.

TIP: The standard invoice layouts available with Sage 50 Accounts automatically show the negative item lines. If you use a customised invoice layout, you can edit it to show negative item lines. Read more

1. Create an invoice as normal.
2. Click the next available item line then for a service invoice, enter some details and press F3. For a product invoice, click the arrow and double-click a special product.
3. Click the Make negative check-box.
4. For the Unit Price, enter the amount as a positive value.
5. Complete the item line details, then click OK.
6. Enter any other items as required.
7. Click Save, then click Close.
   
   

NOTE: The value of the negative items shouldn't exceed the total value of the positive items on the invoice. If you use the VAT Cash Accounting scheme, then the total value negative items for any tax code shouldn't exceed the total value of that tax code.