Follow these steps to duplicate a bill as a debit note:

1. Open the Moon Invoice application on your device or tap on this link.
2. Go to Purchases > Bills from the left menu.
3. Select the bill you want to duplicate.
4. Click on the three-dot (⋮) menu in the top-right corner of the bill.
5. Click on Duplicate and choose As Debit Note from the dropdown.
6. Your bill will now be duplicated as a debit note.