Type field is required for Item CREATE/UPDATE requests for Minor Version 4 or above.
QuickBooks Online only supports three item types: Inventory, Non-inventory and Service. Any item of a type that is not of the three listed will cause this sync error.
In this example, Item "Chartwell Escrow" is a Discount type, which will cause the sync error:
Edit the item with the error to be of type Inventory, Non-inventory or Service and sync. To avoid the error in the future, only create items of type Inventory, Non-inventory or Service.