Вызов функции Delphi с аргументом Pointer на C#

[StructLayout(LayoutKind.Sequential)]
public struct HSECLIB__
{
       public int unused;
}
 
[DllImport("SecLibrary.dll", CallingConvention = CallingConvention.StdCall)]
static extern uint SLUpdateMemoryHash(HSECLIB__ hCtx, IntPtr bytePointer, uint nDataSize);

class Sender
{
    public Sender()
    {
        HSECLIB__ hSecLib2 = new HSECLIB__();
        string sFileIn = @"e:\text.txt";
        string sFileOut = @"e:\text.sign";
        FileStream fsIn = new FileStream(sFileIn, FileMode.Open);
        FileStream fsOut = new FileStream(sFileOut, FileMode.Create);
        long bufSize = fsIn.Length;
        byte[] byteBuf = new byte[bufSize];
 
        int countRead = fsIn.Read(bytePointer, 0, bufSize);    
 
        IntPtr unmanagedPointer = Marshal.AllocHGlobal(byteBuf.Length);
        Marshal.Copy(bytePointer, 0, unmanagedPointer, byteBuf.Length);
 
        int rez = SLUpdateMemoryHash(hSecLib2, unmanagedPointer, bufSize); //В чем ошибка?
        //if (rez != 0) { WriteLog("Ошибка SLUpdateMemoryHash"); }
 
        byte[] outBytes = new byte[bufSize];
        Marshal.Copy(unmanagedPointer, outBytes, 0, byteBuf.Length);
 
        fsOut.Write(bytePointer, 0, outBytes.Length);
        fsOut.Flush();
        fsOut.Close();
        fsIn.Close();
    }
}

byte[] byteBuf = new byte[bufSize];
var handle = GCHandle.Alloc(byteBuf, GCHandleType.Pinned);
IntPtr ptr = GCHandle.ToIntPtr(handle);
rez = SLUpdateMemoryHash(hSecLib2, (IntPtr)handle, 21);
handle.Free()