Voiding or deleting an invoice does not remove it from existence entirely, but rather archives (hides) it. This is standard practice for auditing purposes, as it helps to protect your business from errors or fraud.
Here are the steps to void an invoice in Bookem:
Go to Accounts - Invoices.
Select and open the invoice you want to void.
Delete the allocated payment, by scrolling to the bottom of the invoice, selecting the Payment and Delete
Once the payment(s) have been deleted, click on the Status drop-down menu and select Void, then Save
The invoice will now be voided, you can view the voided invoices by going to Accounts - Invoices and toggling Show voided at the top right to on.