Room Type Code = The code used to identify the room in reservation messages
Inventory Type Code = The code used to identify the room when Inventory updates are received from your system.
It is common that for the PMS the Room Type Code and Inventory Type Code are the same.
Inventory Type Code (InvTypeCode) is used in OTA_HotelAvailNotifRQ and OTA_HotelRateAmountNotifRQ.
Room Type Code (RoomTypeCode) is used in OTA_ResRetrieveRS.