There is a bug in the Stripe documentation. It gives an incorrect code example for trying to reuse an existing card. Here's the fix.

Stripe SCA: Charging Saved Card JS.js

/**
 * There is a bug in the Stripe SCA documentation for reusing saved cards.
 * It gives an incorrect code sample for trying to reuse an existing card via Card Elements.
 *
 * The offending sample: https://stripe.com/docs/payments/cards/charging-saved-cards#submit-payment-automatic-confirmation
 */
 
/** It says to do this **/
cardButton.addEventListener('click', function(ev) {
    stripe.handleCardPayment(
        clientSecret, cardElement, {
            payment_method_data: {
              billing_details: {name: cardholderName.value}
            }
        }
    ).then(function(result) {
        if (result.error) {
            // Display error.message in your UI.
        } else {
            // The payment has succeeded. Display a success message.
        }
    });
});

/**
 * When you should actually do this
 *
 * You don't need to create a card element when reusing a card.
 * Instead pass in the clientSecret and the payment method.
 */
cardButton.addEventListener('click', function(ev) {
    error.style.display = "none";
    stripe.handleCardPayment(
        clientSecret, {
            payment_method: '{{PAYMENT_METHOD_ID}}'
        }
    ).then(function(result) {
        if (result.error) {
            // Display error.message in your UI.
        } else {
            // The payment has succeeded. Display a success message.
        }
    });
});