The OTA_HotelInvCountNotifRQ message is used to communicate room level inventory values to client systems. Each message contains inventory for one or more room types for one hotel for one channel. 

The ARI Sync-Inventory (HTNG) is used to notifiy a booking source of the inventory amount available at a specific hotel property.

The ARI Sync -  Inventory (OTA) is used to notify a booking source of the inventory amount available at a specific hotel property.

The Get Room Inventory Count (OTA_HotelInvCountRQ) API provides the ability to request all room counts by room type and date.