Instagram API, how we communicate with Instagram, only support single photo & video posts. At the moment speaking they don’t have any plans to support carousels and stories.
What Later, Hootsuite etc do is send you a reminder / push notification on your phone (if you download their mobile app) for the posts that cannot be supported automatically via their API. It’s a semi-automatic solution as you have to click the notification (which will take you to Instagram) and publish the post/story.
This is the same solution that we will offer once we have the mobile app.