If I wrote "veggies" on an English paper in University, I guarantee you, it would be marked "wrong" as being "sloppy". However, in academics, they prefer us to use certain words as being more "official". Maybe I just got the wrong Professors and teachers. I had one teacher marked "wonderment" as wrong. But when I showed it to him in the dictionary, he changed his mind, but then tried to argue that it still wasn't "proper" because it referred to a very specific situation. :P Yes, I run into those types. In this case, he would have argued, that because it is a thesis and that is colloquial, it is not "proper" to be used in this situation. And no, he was only a high school teacer.
OTOH.... Update: Merriam-Webster, merely calls it a "variant". Its first known use was in 1955.
Ik heb groente. (I have vegetables) - Ik heb een groente. (I have a vegetable)
I get so many wrong because I just cannot understand what this man says! Even when I use the slow speech mode I can hear him say something but I cannot decipher what it is. It sounds as if he has cotton wool in his mouth! He is spoiling my enjoyment of this course. The lady I understand perfectly.
I don't know exactly how strict Duo is, but in my experience, a single spelling error is allowed as long as the incorrect word is not equal to another word you learn on Duolingo. For instance, often I want to type the word "are" but mistype and spell "ate". That's not allowed because "ate" is also a word you learn.