Either FFP is the rules or its not. If it is it must be enforceable and the FA are entitled to see the relevant documentation.
Manchester City are withholding evidence that is the point of the thread not who can afford what
If they ate entitled to the relevant documentation, then it shouldn't be difficult to enforce, no? That said, FFP is more a UEFA thing, not really FA, I am not too sure. For info, City are going for Grealish for 100m and then apparently for Kane, maybe for even more. So don't know where FFP fits in