Hello Chris Rossen,

I am really sorry for the delay of this reply as it is a weekend for us here.
The reason that you are hitting this error is because you have either changed your password on Facebook or the token has expired. Proceed to the auto posting section at the back end of your site, and revoke the access for Facebook. Then, click on the sign in with Facebook button again and see how it goes.

If still the same, is it possible provide us with your Joomla backend and Facebook access so we can help you check on this issues? Please advise.