If you're having trouble adding or connecting your Facebook page to Post Planner, don't worry.
You can continue using Facebook Business Manager, but you'll need to take the steps below to get connected.
How Post Planner and Facebook Work Together
Everything you do in Facebook is tied to your personal profile. When you sign up for Post Planner, we use Facebook login that's also tied to your personal profile.
That means you authorize your pages and groups through your personal profile, not your business manager.
How to Get Your Facebook Pages Connected to Post Planner
If you're using Facebook Business Manager and want to connect your pages to Post Planner, you'll need to login to Facebook first.
Once you've done this, switch from using Facebook as Business Manager (your page) to using Facebook as yourself. (back to your personal profile)
Once you do that, you can login to Post Planner (authorize your account) using your personal profile which will then pull in all Pages and Groups you administer.
Your Final Steps
Now that you've completed that step, go to Settings - Social Networks and activate the profiles you'd like to post to within Post Planner.
Hover over any page or group and click on it. This will activate that account and allow you to post to it via Post Planner.