Hi,
Can you check the the parameters are available at the REST endpoint. To do this go to:
https://<your geoanalytics machine.domain.com>/<geoanalytics web adaptor>/rest/services/System/GeoAnalyticsManagement/GenerateManifest
There you should see a list of parameters (such as action, dataStoreItemId, and a few more). If you do not see these parameters, try and restart the GeoAnalytics Management tool box using admin at: https://<your geoanalytics machine.domain.com>/<geoanalytics web adaptor>/admin/services/System/GeoAnalyticsManagement then use the stop button, once that is comepleted, use the start button.
If the parameters still don't show up please contact support, and we'll make sure to update the solution here once we figure out the problem.
-Sarah