It sounds like you’re running into an issue posting to Facebook from your app. The error message indicates that your app may not have the right permissions to post to the group or page you’re trying to post to.
A few things to check:
Make sure your app is installed in the group/page you want to post to. To post to a group, your app needs the publish_to_groups permission. To post to a page, it needs both manage_pages and publish_pages permissions.
Double check that the app ID and user ID you’re using are correct and correspond to an app/user with appropriate permissions. The app ID and user ID should be different.
It can take up to 8-10 weeks after submitting your app for review for all features to be enabled. So if your app was just approved, some functionality may still be limited until the review is fully complete.
Some things to try:
Request the publish_to_groups and publish_pages permissions when getting your user access token if posting to groups/pages.
Make sure your app is in “Live” mode, not just “Development” mode.
Try posting as an admin user of the group/page if you haven’t already.
Let me know if those suggestions help or if you’re still seeing issues! The review process can definitely take some time and trial/error.