Put a tablet out at the event and let guests book their own add-on sessions, with no staff login on the device.
Prerequisites
Once you've added services and slots, click "Tablet kiosk" to open the tablet panel: it shows the guest booking link with a Copy button and a QR code you can scan straight from the iPad.
Open the link in a private/guest browser window on the tablet (so no staff account is reachable), and optionally lock the iPad to that page with iOS Guided Access (Settings → Accessibility).
Use the "Waiver" button to set an optional waiver — include your venue name (and therapist names if your insurer needs them); guests must read and sign it (type their name) before booking on the kiosk, and the signed text is saved with their booking.
Guests tap an open time, enter their name and email, and book themselves in; capacity is enforced so a slot can't be overbooked.
Every guest gets a confirmation email straight away with the time, the practitioner, the room and the amount — a retreat guest books on a tablet and walks away with nothing otherwise — plus a pay link if they have not paid yet.
Staff bookings made with "+ Add booking" send the same email.
Guests who pre-pay online instead get theirs once the payment clears (not while they are still on the Stripe page), and paying later with "Mark paid" does NOT send a second one, so nobody receives two confirmations for one session.
After they book, the confirmation screen behaves in one of two ways: a free booking auto-returns to the schedule after about 25 seconds so an unattended tablet resets itself, while a PAID booking keeps its "Pay now" QR code on screen until the guest taps "Done — back to schedule" (or "I'll pay later"), so the code never disappears mid-scan.
Guests can also change their own plans without finding staff: a "Manage my booking" button on the kiosk lets a guest enter the email they booked with to see their own upcoming bookings for this event, change the time of one, or cancel it.
"Change time" is the one to reach for when someone just wants a different slot — the guest picks the new time first and only then lets go of the old one, so nobody loses their spot to the next person at the tablet while they decide, and their signed waiver and details come with them.
Only times costing exactly the same are offered, which is why a PAID session can be moved by the guest too: no money moves either way.
If the new time fills up in the seconds before they confirm, the change is refused and they are told they are still booked at their original time.
Either way the guest gets an email with the new details, so the time in their inbox is never the old one.
Finally, the Tablet kiosk panel has a "Payment QR codes" section: printable codes — one for the whole event plus one per practitioner — that a guest can scan later to look up (by their booking email) anything they still owe, including past sessions, and pay by card with an optional tip.