I developed this app on Nitrous.io (using a heroku postgresql DB). Omniauth works correctly when tested on that platform. When I try on production Heroku, I get a "The parameter app_id is required" error from facebook.
inside devise.rb
config.omniauth :facebook, ENV["FB_APP_ID"], ENV["FB_APP_SECRET"]
My facebook developer site url's and callbacks are up to date. ENV variables are by Figaro, and again, it works fine when run through Nitrous.io.