get http://gooru.org/api/nucleus-index-tracker/v1/access-catalog/
Given a content type, catalog export starts and returns the status and message to check back after sometime. When user checks back again after sometime using the same API, returns the current status and message. If file is ready, message will include download URL to download the exported catalog file.
Once you get the "ready" status in response, you can use the URL contained in "message" field and download the file.