If a payable entry, either expense or inventory, needs voided this is done in the Payable Invoice screen.  Go to AP - Payable Invoices

Locate the invoice and choose Void

Voided Payable for Inventory

When a payable has been voided for an inventory purchase the PO is marked as unpaid and is available in the system to create a new payable entry for.

Entries that are ineligible to void

If a payable’s associated payment method, such as a check or ACH, has been cleared via the Bank Reconciliation process, the associated payable can’t be voided.