Several European Countries are going to a route where invoices are comunicated electronically to the taxes office and changing an invoice after being issued is a crime that is easily detected (supplier and buyers invoices/credits have to match)
The only way to void an invoice is trough a credit note (wich after being issued can’t be altered too).
I looked the Invoice Plane Demo and havent seen any way to issue a credit note. Only invoices.
Credit notes related to specific invoices would be a nice feature.