You can’t delete invoices that are locked to a vat return but you can credit-note them (under “more options” on the invoice details page), just make sure you keep notes to explain what you did if you get inspected.
You can’t delete invoices that are locked to a vat return but you can credit-note them (under “more options” on the invoice details page), just make sure you keep notes to explain what you did if you get inspected.