Reserve (temporarily hold) a specific booking slot for a Cal.com event type via API v2, then release or extend the hold before it auto-expires.

Documented steps

1. Set header cal-api-version: 2024-09-04 on all /v2/slots/reservations requests; omitting it falls back to an older API version.
2. Optionally set Authorization: 'Bearer <API_KEY_OR_ACCESS_TOKEN>' — auth is optional for reserving, but required if you want to control reservationDuration; unauthenticated reservations get the default 5-minute hold.
3. Send POST https://api.cal.com/v2/slots/reservations with JSON body containing required fields eventTypeId=<number> and slotStart=<ISO 8601 UTC datetime, e.g. 2024-09-04T09:00:00Z>.
4. Optionally include slotDuration=<minutes> to override the event type's default length, and reservationDuration=<minutes> (authenticated only) to control how long the hold lasts.
5. Expect HTTP 201 with {status:'success', data:{reservationUid, slotStart, slotEnd, slotDuration, reservationDuration, reservationUntil}}; store reservationUid.
6. To verify a hold is still active, GET https://api.cal.com/v2/slots/reservations/{reservationUid} with cal-api-version: 2024-09-04; data is nullable if the reservation expired.
7. To extend or change a hold, PATCH https://api.cal.com/v2/slots/reservations/{reservationUid} with cal-api-version: 2024-09-04 and body fields eventTypeId and slotStart (both required), plus optional slotDuration/reservationDuration.
8. To release the hold explicitly (user abandoned checkout), DELETE https://api.cal.com/v2/slots/reservations/{reservationUid} with cal-api-version: 2024-09-04; expect HTTP 200 {status:'success'}.
9. If never released, the hold expires automatically at reservationUntil and the slot becomes bookable again.
10. Create the actual booking via POST /v2/bookings before reservationUntil elapses, or the hold is lost.
11. Docs: https://cal.com/docs/api-reference/v2/slots/reserve-a-slot