Why did Google Calendar book a call when my co-host was busy?

A customer books a consultation that needs both the account manager and the technical lead. The link offers a time, but the technical lead is already in another meeting. Now someone has to ask the customer to choose again. Google's existing appointment-schedule guide flags an easy detail to miss: adding a co-host does not make the schedule check that person's availability by default. It tells you to include co-hosts' calendars in the availability checks to prevent double-bookings. Naming someone on the appointment and finding a time they can attend are separate steps. Before sharing a two-person booking link, I would check those settings, then look at the booking page with a known busy slot on each person's calendar. That is a setup check I would make, not a test I have run. Some appointment-schedule features require an eligible subscription. If the technical lead is only needed for certain consultations, give those a separate schedule rather than reserve their time for every introductory call. Which meetings genuinely need both people there?