Welcome to the forum!
Could you please clarify with which app you are having troubles - Facebook or Facetime. Your title says Facebook but the body of your post says FaceTime. They are two different things...
Before we start helping/typing, it may be best that we know for sure where your problem is. Oh, and please give more detail than [the app] doesn't work. What's the behavior, or not, of the iPad? What type of iPad do you have. Did this just start or was it after an update/upgrade. With more details, we probably can narrow your problem down better. Thanks.
Marilyn