You can set a due date for an invoice in Moon Invoice easily by following the steps below.

1. Open the Moon Invoice application on your device or tap on this link.
2. From the main menu on your left, go to Sales ➜ Invoices.
3. Open the existing invoice and tap the Edit icon.
4. Then, select the desired date under the Due Date section on the right-hand side.
5. Click on Save to apply the changes.