If your Facebook Group posts are failing and you're getting error #200 on your failed posts, then this is due to Facebook update from 2018.
In order to proceed with posting, you (as Group admin) must add the Post Planner app to the Group settings. This is a one time process that will allow Post Planner to post to a Facebook Group on your behalf.
Take the steps below to add the app to your Facebook Group.
1. Refresh your Facebook token
Login to Post Planner
Go to Settings > Social Networks and click "Refresh" on the Facebook row
Accept/allow ALL permissions
You can also do a full reset of your FB connection: full instructions for FB reset here
2. Add the Post Planner app in your Group settings
Open the Facebook Group you want to publish to with Post Planner
Scroll down in the left sidebar and click "Settings"
Scroll down (all the way to the bottom) to "Apps" and click pencil "edit" icon
Click the blue "Add Apps" button on the popup that appears
Type "post planner" in the search field and select the Post Planner app card that appears
Click the "Add" button
3. Refresh your FB connection one more time
Repeat Step 1 (refreshing your FB connection) above in Settings > Social Networks.
You're all set!
You've completed the one time authorization required by Facebook and now have the ability to post to your Group.
The error #200 should stop immediately.