If you have opted to take credit cards for client booking and for whatever reason a cancellation and refund is required, you will need to do this directly via Stripe.com . Please log into stripe with the login details you created when activating card payments and from there you can find your customers payment by using the search bar at the top of the screen:
As of August 2021, refunding payments directly from your administration area is on our roadmap pending to Stripe supporting this.