Well ... anyone can be sued, if there is the least shred of possibility that it’s valid. If there is absolutely no basis at all, and it’s apparent from the “get-go” - then something will be “thrown out” - but other than that - the lawsuit will go ahead.
HOWEVER “winning” the lawsuit is a completely different matter. And no, they can’t win it - if you expose a fraud and they can’t prove it’s not a fraud - and you can prove it’s a fraud. SO ... the bottom line is that you will prevail in a lawsuit!
But, the other “bottom line” to this issue - is what the Founding Fathers thought about “Free Speech” - in that it’s “free speech” itself which will be what “argues against another’s free speech” - in which that other free speech is FALSE.
The idea here is that truth always rises to the surface and lies sink to the bottom - if all things are equal and the government does not intervene and try to “maintain” one kind of speech over another.