Can’t access old account (Facebook)

In the past I have always logged in using the log in using Facebook feature. Whenever I do that now, I get an error on Facebook. “App not setup”. I’m not sure what that means but all of my old posts were through the Facebook login option which now seems broken. I am using an iPhone, if that information helps. Any help steering me in the right direction is greatly appreciated.

Help me Obi-wan Kenobi. You’re my only hope.

 

I don't come in through Facebook (don't even have an account) so the best thing I can suggest is you log straight in here. If you don't know your password you can use the 'Forgot Password' and your email address (NOT your user ID) and an email should be sent to you with instructions.
Anyone else who has used Facebook to log in and has a better suggestion feel free to respond.