The act of an agent communicating (service provider, social media, etc) their arrival by registering/confirming for a previously reserved service (e.g. flight check-in) or at a place (e.g. hotel), possibly resulting in a result (boarding pass, etc).\n\nRelated actions:\n\n [[CheckOutAction]]: The antonym of CheckInAction.\n [[ArriveAction]]: Unlike ArriveAction, CheckInAction implies that the agent is informing/confirming the start of a previously reserved service.\n [[ConfirmAction]]: Unlike ConfirmAction, CheckInAction implies that the agent is informing/confirming the start* of a previously reserved service rather than its validity/existence.