Voiding will remove invoices from all financial reports. If there is a payment allocated to the invoice, the payment will need to be deleted in order to void the invoice.
However, if an invoice has been included on a VAT return you will not be able to void this invoice unless you are able to delete the return. You can instead reverse the invoice by applying a credit note against an unpaid invoice or by creating a refund to negate a paid invoice.
Voiding an Invoice
Navigate to the Sales > Invoices > All menu and click on the invoice number of the invoice that you would like to void.
Click on the Void button and confirm when prompted.
If there are any payments allocated to the invoice you will be prompted to delete either the payment or both the payment and the invoice.