Unfortunately, due to Facebook API restrictions we're unable to schedule and publish content on Facebook Personal Profiles. Starting from August 1st 2018, publishing to Facebook profiles via third party apps has been suspended by Facebook
As you know, Facebook is on a mission to improve their platform and reduce abuse and this change is part of that mission.
The good news is that you can turn your Facebook profile into a page and continue using Planable, here is how. Afterward, you can connect this page in Planable.