Your ゆ is a big ゆ and not a ゅ. What you wrote is niyuu rather than nyuu.
From the FAQ:
Why is my reading answer for 入 (にゅう), 上 (じょう), 九 (きゅう), 力 (りょく), 十 (じゅう), or 女 (じょ) being marked incorrect? I’m putting in the right answer!
Most likely, you are putting in a big や, ゆ, or よ instead of a small one. See the difference?
にゆう = niyuu
にゅう = nyuu
じよう = jiyou
じょう = jou/jyou
きゆう = kiyuu
きゅう = kyuu
りよく = riyoku
りょく = ryoku
じゆう = jiyuu
じゅう = juu/jyuu
じよ = jiyo
じょ = jo/jyo
The difference is big, and it’s important to get these correct. For example, じゆう means “freedom,” so if you wrote that in instead of じゅう you would be saying something completely different.