You can add your own invoice number series 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 select the Edit option. 
4. Manually enter the invoice number.
5. Finally, click the Save option to apply the changes.

Note: When you create a new invoice, the invoice number will automatically follow the existing number sequence - no manual entry needed.