"Sorry", you don't usually care about punctuation at all! So why are you insisting on the quotation marks?
I don't know why. This is something that is run by the Duo machinery, not created by us course creators. It shouldn't complain about the quotation marks here, but sometimes the machine gets fussy where it shouldn't.
It's embarrassing that this still doesn't work the way it's supposed to, but we cannot do anything about it. Hence, I have marked this sentence for removal in the next tree. We'll make sure not to stick anything with quotation marks in that tree version.
Why not 'must' instead of 'have to'. And why the insistence on punctuation as others say?
"must" is also accepted, actually, but if Duolingo arbitrarily decided to require quotation marks from you, then it probably also decided to show the default translation of "have to" rather than the equally good "must".
Feb. 5, 2018 - Now it not only requires quotation marks around "ja" but also requires "ja" be underlined _.! Today I was using my cellphone working on making my tree golden, and I could not do the to satisfy Duo and complete the strengthening exercise!!! So very frustrating. Also, while working on my desktop computer, Duo advised me of a typo for not having the ____.