There are no docs. All I got are the dll and some C# examples like this:

[DllImport("FFACE.dll", EntryPoint = "GetInventoryItem")] public static extern INVENTORYITEM InventoryItem(int index);

and the working statment:

INVENTORYITEM x = FFACE.Inventory.InventoryItem(1);

Thats about it. Next to that I got the fface.h file (which is outdated).

The C# and the JNA run against the same dll and the dll access a running application. I do let both run with the same running process of that application. I am using the same parameters in C# and JNA.

I tried even to change the JNA method to use a single parameter only aswell as the C# implementation does. The return value still was empty.