The existing API used to export organization level users is https://developer.atlassian.com/cloud/admin/organization/rest/api-group-users/#api-orgs-orgid-users-get, and when exporting all the users of the org into CSV from the UI from the steps below:

• Directory >> Users >> Export Users
  we get a field "added to org" showing the date the user was added to the org.

The same field does not show up when we are using the API (mentioned above)

The current workaround is to use the below API
https://admin.atlassian.com/gateway/api/adminhub/um/org/<orgID>/exports/users, updating the session cookie and Content Type set to application/json in the Headers section

Body:

{ "includeApplicationAccess": "true", "includeGroups": "true", "includeInactiveUsers": "true", "selectedGroupIds": [] }

Creating this feature request to add "added to org" field in the existing API response