Just to add…
With Monzo you’ll need to contact them advance, ideally the day before and ask for a limit increase via chat. Or you can attempt the payment, watch it fail, then it should prompt you to request a higher limit.
I’d also encourage the other person to be on standby to ring their bank, because that volume will almost certainly trigger a fraud flag. That can delay things by a few hours.
Obviously, don’t actually transfer anything until you’ve signed for the car etc but you knew that already