I noticed this on the Facebook Credits Terms page:
You cannot have a cross-application virtual currency that can be purchased with Credits, so you may not accept Credits as payment for a virtual currency or other stored value item that can be used outside of the application where the payment was completed.
I want my game to work on Facebook, Kongregate, mobile platforms, and possibly my own website. I plan to use a universal virtual currency say XCash. I was wondering if I can have players pay with Facebook Credits for XCash and this XCash can also be purchased through the other platforms such as on Kongregate with Kongregate credits, or through my website through a credit card system without violating the Facebook Credit Terms.