How do I stop a follow-up campaign once the person books an appointment?

You do not need if/else conditions on every step. Build a small separate workflow that stops the campaign:

1. In the same agent, create a new workflow and give it a clear name, for example Appointment booked.
2. Set the trigger to Appointment booked (appointment scheduled) and choose the calendar the bookings go on, for example your free inspection calendar.
3. Add a Deactivate from workflow step and set it to deactivate from all workflows in this agent.

Now when someone books, including when the AI agent books for them, the outreach workflow is cancelled and they do not get the next message. This also covers people who already responded, and it is easier than building branches for clicked, did not click or responded. You can also set the contact's pipeline stage in the same workflow so you can see they have booked.

Branching on whether you got a response is also possible in the workflow builder, and it is good practice so contacts do not keep getting the same message.