Select the customer first. On the payment page choose Customer Card on File — the modal lists their saved cards with an Add card button, pick a card and press Checkout. Alternatively choose Enter Card Number to type a one-off card. If Sprwt has turned on 3D Secure for your Stripe integration, the customer's bank may require an extra confirmation step, which is handled on screen before the order completes. Both methods record the payment method as Stripe.