[V8i C# MDL] mdlView_getClipBoundaryElement not working

Hi,

I had an issue on calling mdlView_getClipBoundaryElement() which is the opposite problem of the post below. I was trying this with AECOsim V8i SS6 and VBA approach did work. However, it gave me -168 error code and Element ID as 0 all the time. I've tried different combinations of function signature but all failed, including different data type mappings, ref keyword, calling convention, etc. Any idea? Thanks.

https://communities.bentley.com/products/programming/microstation_programming/f/microstation-programming---forum/138063/v8i-c-mdl-mdlview_setclipboundaryelement--168-mdlerr_noclipvolume---help

My code for reference:

[DllImport("stdmdlbltin.dll", CallingConvention = CallingConvention.Cdecl)]
internal static extern IntPtr mdlView_getClipBoundaryElement
(
ref UInt64 pElementId,
Int32 viewIndex
);

ulong eId = 123;
int status = mdlView_getClipBoundaryElement(ref eId, 1).ToInt32();
MessageBox.Show(status + ": " eId);