Instagram's API has several limitations for all scheduling tools.
Here's everything you need to know about how you can get access to Direct Publishing (posts going out automatically):
You need to have an Instagram Business account. Find out here how to easily switch a personal profile to a Business page.
Make sure your Instagram Business page is linked to a Facebook page
You can directly publish only Instagram single image or video feed posts that are between these ratio ranges*:
Between 4:5 and 1.91:1
Between 4:5 and 16:9 (up to 60 sec.)
For stories and the following types of accounts (personal profiles, creator accounts, or business accounts not linked to Facebook) you can publish using our mobile app.
Learn here how to disable direct publishing.