The Contra feature in MoneyWorks is referring to contra a credit note against an invoice for the same debtor or creditor. You can’t use the Contra feature to contra invoices between a debtor and a creditor.
From the Command menu, select Adjustments and follow by the Contra Invoices function to contra a Credit Note against an Invoice. From the Contra Invocies Window, highlight the Credit Note and click the Continue button to proceed with the contra process.
Next, you select the Invoice to contra. MoneyWorks will list out all the unpaid invoices which belong to the same debtor or creditor as of the credit note that you had selected earlier. Then, continue and complete the contra process.