"Umechukua matunda yapi?" should have been accepted. (It couldn't be reported because it was judged to be spelling mistake.)
fruits plural? so why not watunda wepi? Me soooo confused!
Think noun class: tunda/matunda is ji/ma class and refer to Machieng's noun class table: https://forum.duolingo.com/comment/32745349. Hence, tunda lipi, which (piece of) fruit, and matunda yapi, which fruit.
Asante sana Ernst!