How do I create/update an Excel file using the API?

Hi,

I've successfully created a "Web Intelligence" document using the API (POST /raylight/v1/documents).  However, I need to do the same for an Excel file type and have been unable to do so.  Attached are the different steps needed to accomplish this with the UI.  I need to be able to do the same thing through the API.

I searched through the docs but haven't found anything regarding this particular aspect.

Does anyone have a clue? 

Thanks