Overriding image width with updateExportSettings

Question

Writing my first lightroom plugin, I have created a minimal example which should set the photo width here and included below. However I can not get the image to be the 400 x 400 specified.
ExportFilterProvider400.lua
local LrView = import 'LrView'
local bind   = LrView.bind
-- This function will create the section displayed on the export dialog
-- when this filter is added to the export session.
local function sectionForFilterInDialog( f, propertyTable )
  return {
    title = LOC "$$$/SDK/MetaExportFilter/SectionTitle=400x400 Filter",
end
-- Example on updating export settings
local function updateExportSettings( exportSettings )
  exportSettings.LR_size_maxHeight = 400
  exportSettings.LR_size_maxWidth  = 400
  exportSettings.LR_size_doConstrain = true
end
return {
sectionForFilterInDialog = sectionForFilterInDialog,
updateExportSettings     = updateExportSettings    , --Does this works
Info.lua
return {
  LrSdkVersion        = 3.0,
  LrSdkMinimumVersion = 1.3, -- minimum SDK version required by this plugin
  LrPluginName        = "400x400 Export",
  LrToolkitIdentifier = 'sample.export400x400',
  LrExportFilterProvider = {
    title = LOC "$$$/SDK/MetaExportFilter/Sample=400x400 Size", -- the string that appears in the export filter section of the export dialog in LR
    file  = 'ExportFilterProvider400.lua', -- name of the file containing the filter definition script
    id    = "metadata1",  -- unique identifier for export filter
  VERSION = { major=5, minor=0, revision=0, build=907681, },
Adobe Lightroom can load the plugin, and add it to the export session, but the updateExportSettings do not seem to take effect. Tested in Lightroom 5.3.
Thanks

Answer 1

Thanks, Will try this out.
On closer reading the SDK Guide on page 51 does mention:
If the service has defined an updateExportSettings() function, it is called.
and at the end of that secion:
The filters, if any, are not involved at this stage.
Was not aware of the difference of an ExportService plugin and an ExportFilter plugin at the time of reading.
Update:
This is the minimum example I got working Info.lua stays the same:
local function sectionForFilterInDialog( f, propertyTable )  return {    title = LOC "$$$/SDK/MetaExportFilter/SectionTitle=400x400 Filter",  }end --------------------------------------------------------------------------------local function postProcessRenderedPhotos( functionContext, filterContext )   local renditionOptions = {    filterSettings = function( renditionToSatisfy, exportSettings )      exportSettings.LR_size_maxHeight = 400      exportSettings.LR_size_maxWidth  = 400      exportSettings.LR_size_doConstrain = true    end  }   for sourceRendition, renditionToSatisfy in filterContext:renditions( renditionOptions ) do    -- Wait for the upstream task to finish its work on this photo.     local success, pathOrMessage = sourceRendition:waitForRender()   endend-------------------------------------------------------------------------------- return {  sectionForFilterInDialog  = sectionForFilterInDialog,  postProcessRenderedPhotos = postProcessRenderedPhotos,}