Good question. The most likely reason is that something has changed client side, resulting in the Facebook token being invalid. We will need to resolve this error - usually a permissions error - before manually activating your lead lists and resending any unsent leads. If worst comes to worst, we will need you to disconnect Facebook from Driftrock and reconnect it. The person who does the reconnection must have admin-level permissions else the lead lists will be paused due to permissions errors.