When you enable a Stripe form on your checkout page, you have the option of only collecting the customer's card details at the time of checkout rather than charging the card at that time. This may have the effect of increasing sales and reducing cart abandonment by your visitors.
This option can be set by clicking Website Booking Form Setup and then navigating to the Booking Form Settings page, and modifying the 'Charge Option' to be Collect Card at Checkout.
With this option set, before being able to complete the checkout, Stripe will confirm that the customer's card is valid, however there could be problems with the card, such as insufficient funds, that prevent the charge from going through when you go to charge it, typically after the service or goods have been delivered to the customer. In this case, you either need to set a new default card or collect payment using other means.