Invoicing Basics - Sales Invoice

By adding your VAT number to the document's template. By adding your company's details to the document's template. By adding them to your company's data in the main settings. By requesting Obi-Wan Kenobi's help.

By clicking on "edit" in the invoice's form view. By clicking on "cancel invoice" in the invoice's form view. By duplicating the invoice and deleting the original one. You can't alter a validated invoice, but you can add a credit note, in the invoice's form view.