How to Write Off a Bad Debt
To write off a bad debt, click menu File > New > Credit Note. The Credit Note window will be shown:
Enter the same details as for a credit note, except use 'Bad Debts Expense' in the Account column. The VAT details should be the same as the invoices being written off.
Click OK to save the credit note.
Now you need to allocate the credit to the outstanding invoices. Navigate to the Invoices list (menu Window > Invoices) and select the credit note you just created. Then click File > New > Allocate Selected Credit:
Tick the invoices you want to write off and click OK.