I do not want the last purchase of 79.99 please stop payment.

You cannot. Once a purchase has been initiated, it must complete. There is no way to stop it.

You can, once the purchase has been successfully charged to you, request a refund: Request a refund for apps or content that you bought from Apple - Apple Support

If this is a subscription, you will need to cancel it before you can request a refund: See or cancel your subscriptions - Apple Support