Why can’t I edit or delete a processed transaction?

A processed transaction has financial implications. Also, a transaction from a subsidiary ledger has a server posting to other ledgers. For example, an invoice posts to the sales audit trail, the nominal ledger audit trail, and the vat return audit trail. Modifying just one of these transactions on their own will create an imbalance, with no record of what happened. In addition, it is illegal to change any details of an invoice issued, keeping the invoice reference number the same.