Translation:Bhuail an carr glas an balla mór.
Strictly speaking, there isn't anything wrong with it -uaine doesn't seem to be part of Duolingo's vocabulary, though.
If the question comes up again for you, you can report it so that it can be added as an acceptable answer in the future.
Both terms refer to the color "of the growing grass". But very few people still use uaine (used in the Constitution). Uaine tends to refer to a vivid, often artificial, green. For most Irish people it sounds dated I suppose... I like it though...
I don't think glas should be lenited there (please correct me if I'm wrong) but otherwise it seems like it should be accepted.
Buail is a verb that should be used with the preposition le. Unclear why leis an balla mór is wrong
One of the many Irish verbs that has very different meanings when paired with different prepositions. Worth looking in a good dictionary just to get a flavor for it. Buail amach, buail ar, buail le, buail suas, buail chuaig, buail um, buail faoi... If you really wanna blow your mind, check out verbs like bain or cuir to see how many different meanings can come from one verb matched with different prepositions.
Buail is a verb that is used with le to mean "meet". It has a different meaning, "strike", without le. Bhuail an carr uaine leis an mballa mór means "The green car met the big wall, not "struck".