In Odoo, it's not possible to modify an invoice that has been validated and sent to the customer. If a mistake was made on a validated invoice, the legal way to handle that is to refund the invoice, reconcile it with the original invoice to close them and create a new invoice. and we can see the refund option in vendors so basically, it is a credit note from the vendor. Odoo creates a credit note, automatically validates it, reconciles the original invoice with it, and open a new draft invoice prefilled with the same details from the original invoice.