"U heeft niets nodig."
Translation:You do not need anything.
That is an impressive streak! And I highly doubt you're still confused about why the sentence is incorrect, but just in case for others, in your sentence 'need' is a noun when it should be a verb. :)
Because that has a different meaning, namely 'You do not need' and the object is missing. It is the difference between 'not' and 'nothing'.
I have a strong urge to say "u heeft niks nodig", what would be the difference?