"I am not an actor, but a reporter."
Translation:Nem színész vagyok, hanem riporter.
Based on the lesson's explanation, no. Based on my lived experience as a Hungarian, people say it how you've suggested all the time and nobody bats an eye. This is one of those cases where Duolingo is forcing a very precise way of speaking, where in reality in normal conversation the alternative is virtually always accepted.
Yes, it's really not correct.
For "nem A, hanem B", the A and the B have to be comparable.
But your first half of the sentence has nem vagyok, i.e. you are negating "am". (I AM not an actor, but A REPORTER). But the proposed replacement is not another verb, but a noun, riporter. That doesn't really fit.
You probably want to contrast "I'm not AN ACTOR, but A REPORTER" -- so put the nem before the egy színész.
So the issue with this is while it's not correct given the explanation in the lesson, I am Hungarian and have also discussed this with other native Hungarians and the common consensus is that it's perfectly appropriate to say "Nem vagyok X, hanem Y". It might be less formal, however in all my life I've never seen anyone bat an eye at it.
Cool! Fantastic reply, thank you. I had this question a few times before and you gave a simple view on it.
I am native hungarian, and I have used the same form. Nem vagyok színész, hanem riporter. I think both sentence has the same meaning. It should be accepted. There is only a nuance difference between "nem vagyok színész" and "nem színész vagyok". I should always use "nem" before the word which I want to deny. If I want to use negation with /am,is,are/ then I can use the word "nem" almost anywhere. "nem vagyok papagáj / nem papagáj vagyok", but if I want to say, that I'm not afraid of the wolf = 'Nem félek a farkastól', but if I say 'nem a farkastól félek' it means that I am afraid of something, but not from a wolf.