Here are the steps you need to follow in order to turn a voided invoice back to a draft. 

1. Open the Moon Invoice application on your smartphone or tap this link.
2. Go to Sales > Invoices.
3. Tap on the voided invoice you want to change.
4. Tap the More Options (⋮) menu.
5. Click on Mark as Draft to convert the invoice back to draft status.

                                                                                                                                             - Moon Invoice