it's highly likely that the 'credits' does not function properly at all if you are playing online or some modes of this game.
Correct. The Trainer is working just fine with all the DLCs - only the franchise-mode (online-mode) is not, but thats just normal.
Well, sometimes the trainer does not respond for 5 secs after changing credits or money, but it still works. If there would be needed an update, then only for the new Game Version 1.3.2 - but I don't think so.