"A postás nem ember" should be accepted, too, in the sense he is not human but extraterrestial or ogre.
Hmm, but that would be "the postman is not a human" in English.
A postásnő nem férfi is not accepted? Is this a mistake or on purpose? I would have thought that logically, by not being a man, the postman is a woman. (Or trans or something else, but this is a beginner's sentence).
Why isn't "A postes nincs ferfi" correct?
"Nincs" means the absence of something, not a simple negation, which this calls for.