Translation:Pau ka ʻai!
Sorry, Haalilio, but it seems like the gerund marker ʻana is never going to be introduced in DL. I also submitted "Pau ka ʻai ʻana," but at least now it is being accepted with the notation of "Another correct solution" which was their answer as given above. I'm now going through the activities on level 5, so I've pretty much given up on waiting for it to be introduced.
DL seems to rely entirely on simple verbs without ʻana when it should actually be included. For example, "Makemake au i ka heʻe nalu" for "I like surfing" instead of "Makemake au i ka heʻe nalu ʻana." The only place that ʻana has shown up (that I've noticed, anyway) is in the single phrase "Mahalo kēia hui ʻana," and it was never discussed. It was simply identified as a phrase used by Niʻihau speakers.
Too bad. That's a major deficiency in the program, and anyone relying totally on DL for their Hawaiian language instruction will probably never even realize that it exists or how common it is in general conversation (in the "walaʻau ʻana," as you said).
This just emphasizes the truth of the ʻōlelo noʻeau: "ʻAʻole pau ka ʻike i ka hālau hoʻokahi."
Mahalo kou mau manaʻo.