The standing challenge of the Qur'an for about fourteen hundred years is the testimony for the credibility of the prophet Muhammad:
Surah Al-Israa Ruku 10 Surah 17
88 Say: Verily, though mankind and the Jinn should assemble to produce the like of this Qur'an, they could not produce the like thereof though they were helpers one of another.
M. Pickthall Quran Translation
https://answers.yahoo.com/question/index?qid=20130608033430AAebzSw
So the challenge is, that it's not possible for men to write a book like the Koran, even if they are helped by supernatural Djinn? Seriously? That's it?
But that's been met time and time again! What a silly "challenge" to claim. Some of the books "the like of the Koran" are serious, some are fiction, some are satire even. But Many many supernatural works have been put forth, and quite a few of them more coherent and useful than the Koran.
I think JRR Tolkein wrote a much better book than the Koran, and he didn't even have magic Djinn to help him!
And then there's L. Ron Hubbard and Joseph Smith, who wrote books much like the Koran and even got followers just like the Koran.
Confucious wrote a whole lot of useful rules into a book - some of them are out of date and no longer useful (like the Koran, the bible and the Torah) but some are actually still quite wise and useful.
So yeah, this "challenge" is to actual challenges like crayons are to quantum networks.