Additional reasons you can't cancel an invoice are as follows:  You applied a prepayment to the invoice;  Canceling the invoice reduces the billed quantity to less than zero on the purchase order. For partially paid invoices you can create a credit memo and reconcile it with the invoice to turn this invoice into a fully paid invoice.
The invoice is:  Fully or partially paid  On hold  Selected for payment  Matched to a purchase order with a status of Finally closed  Already canceled  Corrected by a credit or debit memo
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I can't cancel an invoice.