CheckoutWC replaces the WooCommerce checkout and thank you pages with its own, and Confetti works with it through the WooCommerce integration rather than a separate one of its own.
Set it up the way you would for any WooCommerce store. How to add confetti to WooCommerce covers the thank you page and discount codes.
CheckoutWC still appears in the Integrations list so you can see it’s recognised, but there’s nothing to configure on it.