How Invoice Voiding Works

Source: invoice.rb:598-689, invoices_controller.rb:838-853

Cannot void an open invoice -- must delete instead (error: "invoice is not processed and can be deleted instead")
All payments must be voided first before voiding the invoice
Cannot void if credits have been applied from the invoice -- error lists which credit numbers are applied
Cannot void internal invoices if the linked vehicle has already been sold
Loan car must be returned (status "C" completed or "X") before voiding
On void: product quantities are restored, purchase orders and vendor invoices are unlinked, items are soft-deleted
Vehicle trade-ins and sales are reversed: trade-in vehicles go back to previous state, sold vehicles return to for_sale with customer reset
Customer balances are recredited/debited to undo the original financial transaction
Serial numbers are detached (invoice_id and invoice_item_id cleared) and each detachment is logged in TransactionLog
Voiding a credit that contained a vehicle sale re-assigns the vehicle to the original sale customer and restores date_of_sale

"It says I should delete instead of void" -> the invoice is still open (not processed); open invoices are deleted, not voided
"I need to void but it says there are payments" -> all customer payments on this invoice must be voided first; go to the payments section
"I voided the credit note and the vehicle went back to sold" -> voiding a credit reversal undoes the reversal, putting the vehicle back in its sold state
"What happened to the serial numbers after voiding?" -> they are detached from the invoice and available for re-use; check the serial number list