When two bookings overlap, first establish whether the same person or resource is genuinely required at the same time. Then trace the booking’s availability settings and source record. Do not move a customer or delete an event until the responsible booker has agreed the resolution.

Diagnose the conflict from one actual booking

Keep the booking ID, creation and change times, appointment time zone, assigned staff and resources, and the calendars consulted. Use those facts to distinguish a scheduling rule from a sync failure.

What you observe What to check Corrective action
An existing event did not block a slot Busy/free status, acceptance status and selected availability calendars Correct the relevant setting and repeat the booking test
The host was free but a co-host was busy Whether the co-host’s calendar was actually included Include the required calendar where supported; otherwise verify availability before confirmation
Two staff appointments use the same room Whether the tool models room capacity independently Configure the resource or use an explicit reservation process
A manual booking overlaps self-service Override permissions and where the manual record was saved Define permitted overrides and reconcile both booking paths
External edits do not update the scheduler Sync direction, connection state and documented edit location Change the source record in the supported system
Times appear different to participants Date, named time zone, daylight-saving conversion and device display Confirm the same instant in each participant’s zone
Adjacent bookings leave no preparation time Service duration, buffer and travel settings Reserve the actual required block

Calendar behavior is provider-specific

Google Calendar appointment schedules: co-host availability is not checked automatically. Select the relevant calendars where the account supports it. Google also says tentative or unaccepted events do not block appointment availability. An event appearing on a calendar is therefore not sufficient evidence that it protects a slot. Setup; availability rules.

Microsoft Bookings: inspect the staff setting that makes events on the Microsoft 365 calendar affect availability. Service hours, staff hours and assigned staff also matter. Staff availability.

Acuity: outside calendar events block time only when that option is enabled, and availability is configured in Acuity. Its documentation lists exclusions, including free events and outside calendars with read-only access. Moving an appointment in an outside calendar is not a substitute for checking the supported Acuity workflow. Calendar sync.

These are different rules. Do not apply Google’s treatment of tentative events to every integration, or assume all connections update immediately.

Resolve, then test the repair

Agree which appointment changes, communicate with affected people, and update the authoritative booking. Check the staff calendar, room or equipment reservation, customer message, and any payment consequence separately. Preserve the reason and owner of the correction.

Reproduce the failure using permitted test appointments: an existing busy event, a co-host conflict, a room conflict and a reschedule are useful cases when relevant. Record the actual results and timestamps. A successful test on one calendar does not verify every staff member’s configuration.

Use the booking checklist for day-to-day checks. Consider changing scheduling software when a required capacity rule cannot be represented reliably, rather than buying a replacement for a repairable setting.