Go to “Settings” > “Business Info” > “Booking & Payment” > Booking Requirements section. Tap “Require Card” to set your rules for appointment booking online. You can require a credit card from all clients who book you online, from new clients or never require.
Note that requiring a credit card does not mean that clients will be charged at the time they make an online booking for you. They will never be charged until you check them out. Requiring a credit card is like making a reservation. What it does is ensure that you’re protected against no-shows and are able to get your cancellation fee if a client is a no-show or cancels last minute.