Years ago, before the Services mobile apps had push notifications, we developed a Facebook app that allowed you to manage your schedule and that sent you notifications for new requests. A couple years ago, we discontinued that app, since our mobile apps had improved and provided all the same functionality and more. Anyone who was still logged in to the Facebook app, however, was still able to receive notifications of scheduling requests, though there was no way to sign up if you weren't already signed up.
Recently, Facebook had a security incident which logged everyone out of the PCO Schedule app. There hasn't been a way to log back in again for a couple of years, and since we discontinued the app, this looks like the end of the line. If you were receiving Facebook notifications for your Planning Center scheduling requests, those will no longer come through. We encourage you to download the Planning Center Services app for iOS or Android and sign up for push notifications.