Require a card to book

Open Menu, then SETTINGS, then Payments and communication, and find the card policy.

The three settings are Off, New clients, and Everyone. The screen notes the dependency: this requires a card to finish online booking, and it needs Stripe connected.

New clients is the setting most people want. It protects you from strangers who book three slots and vanish, without making the regular who has come every six weeks for four years enter a card.