When creating invoices manually or editing existing ones, it is possible to give two invoices the same invoice number. Normally, this is not allowed for companies by business legislations, so maybe the component should integrate this by making the field UNIQUE in the database or at least have some validation mechanism.
Also, it is possible to leave the field invoiceNumber empty, in which case the invoice later cannot be opened again (because the link in the various list views is missing). Marking it as required in the schema could prevent this.
