To cancel any posted invoices, select ‘Cancel or re-issue Posted Invoices’ from the ‘Accounts Receivable’ menu as shown below.
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You will then be presented with the following form.
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From here you can select which transaction number to cancel as well as choose to either cancel the invoice outright, or re-instate it in an un-posted state so that changes can be made to it via Accounts Receivable – Unposted Invoices.
After you press OK the ledger entries will be made to cancel the invoice as requested.
Items that have been reconciled in the bank cannot be unposted.