I've only ever paid cash, so it might be that any sort of financial loan uses a different process. Dunno if you will see a Final Invoice if the car is financed (I think, technically, that when using Finance the invoice is From Tesla to Finance Company in that instance, and then you "Make payments" (for which you would get an invoice, or a "end of year statement" / similar), so perhaps the end user never sees a final invoice in that scenario?
I would expect you to get an Invoice, from Tesla, if you paid a deposit to them direct (e.g. the original £100-ish deposit if you paid that to Tesla and then "converted" you order to Finance)