Instagram Error: Unsupported Post Request

Publishing to Instagram directly is possible for feed posts and reels sent to Instagram Business or Creator Profiles, which are connected to a Facebook Page. 

If you're seeing an error like " Unsupported post request. Object with ID [id number] does not exist, cannot be loaded due to missing permissions, or does not support this operation. Please read the Graph API documentation", that means that your Instagram account is no longer connected to a Facebook Page. 

To Resolve

1. Access your Facebook account, navigate to your Facebook Page and click "Settings" from the left-hand menu on your screen;
2. Select "Instagram", then add an Instagram account by clicking "Connect Account".

Check out How To Switch Your Personal Instagram Profile To A Business Profile for detailed steps.