The ExportApp in the .NET SDK is intended for services running behind the proxy. To do "normal" export you should use the Repository API. You find the instructions here:
do you have an updates on this topic?
I'm trying the exact same thing and am facing also the issue of not understanding the "ids" parameter. Also found the "Array of identifiers. The list of all the objects in the app to be exported must be given. This list must contain the GUIDs of all these objects." explanation, but I'm not sure what to do with it. Tried to pass a List of IDs with all children of the app, unfortunately without success.
Any help is appreciated.