Problem getting correct parameter types for P/Invoke call

Question

Trying to Interop a functionality from the Outside In API from Oracle.
Have the following function:

 SCCERR EXOpenExport {
    VTHDOC    hDoc,
    VTDWORD    dwOutputId,
    VTDWORD    dwSpecType,
    VTLPVOID    pSpec,
    VTDWORD    dwFlags,
    VTSYSPARAM    dwReserved,
    VTLPVOID    pCallbackFunc,
    VTSYSPARAM    dwCallbackData,
    VTLPHEXPORT    phExport);

From the header files I reduced the parameters to:

 
typedef VTSYSPARAM VTHDOC, VTLPHDOC *
typedef DWORD_PTR  VTSYSPARAM
typedef unsigned long  DWORD_PTR
 
typedef unsigned long  VTDWORD
 
typedef VTVOID*   VTLPVOID
#define VTVOID  void
 
typedef VTHDOC VTHEXPORT, *VTLPEXPORT
 
These are for 32 bit windows
 

Going through the header files, the example programs, and the documentation I found:
  1. That pSpec could be a pointer to a buffer or NULL, so I set it to a IntPtr.Zero (documentation).
  2. That dwFlags and dwReserved according to the documentation "Must be set by the developer to 0".
  3. That pCallbackFunc can be set to NULL if I don't want to handle callbacks.
  6. That the last two are based on structs that I wrote C# wrappers for using the [StructLayout(LayoutKind.Sequential)]. Then instatiated an instance and generated the parameters by first creating a IntPtr with Marshal.AllocHGlobal(Marshal.SizeOf(instance)), then getting the address value which is passed as a uint for dwCallbackData and a IntPtr for phExport.
The final parameter list is as follows:

phDoc as a IntPtr which was loaded with an address by the DAOpenDocument function called before
dwOutputId as uint set to 1535 which represents FI_JPEGFIF                                    

dwSpecType as int set to 2 which represents IOTYPE_ANSIPATH

pSpec as an IntPtr.Zero where the output will be written

dwFlags as uint set to 0 as directed

dwReserved as uint set to 0 as directed

pCallbackFunc as IntPtr set to NULL as I will handle results

dwCallBackDate as uint the address of a buffer for a struct

phExport as IntPtr to another struct buffer

still get an undefined error from the API.
Jim