If a slot is taken, can the AI offer a waitlist?

Yes: when a request lands on a full day, the AI offers the next availabilities and, if the caller is in a hurry, the waitlist option — "if someone cancels, you're the first called back". Waitlisted people are notified automatically as soon as a cancellation frees a matching slot, in signup order. You stay in control: the waitlist is visible in the dashboard, and you can turn the option off if you'd rather keep that contact for a personal callback. It's especially useful in high season, when cancellations are your best source of slots.