Here are the steps to enable the total amount in letters.

1. Open the Moon Invoice application on your device or tap on this link.
2. Go to Settings > PDF & Print Settings > Summary.
3. Enable the option Total in Words and tap Save.
4. Once enabled, the total invoice amount will be shown in words on the invoice.
5. This feature works with English and is not supported in other languages.

                                                                                                                                          - Moon Invoice