Translation:The key was not lost
Just to check I put "They key was not lost." Rejected. However, "The key did not get lost" was rejected in favor of "They key did not get lost."
I wish when contributors made corrections in this course they were a bit more thorough. Of course I also wish there were contributors even listed in the Incubator.
Up above, I see it with "the" ... so, it's either been fixed in the last two hours or Duo is a bit glitchy and inconsistent.
How about "didn't get lost"? I thought potea is "get lost" and poteza "lose".
It seems the contributors meant for that to be included, but there's a typo in the system currently. See my comment in reply to saynave's post.
Don't forget to read the previous comments before you post. The discussion above suggests that you might still have to write "they" instead of "the", just because this beta error still hasn't been corrected yet, apparently. Your answer is more correct than the accepted one, though you might also have to write "did not" instead of "didn't", but you can report that too.
If "did not" is accepted, then Duolingo's automated contraction system should automatically accept "didn't." The exception is if for some reason the contributors included the translation with "didn't" directly but left off the one with "did not," since I don't think there's a system to automatically "de-contract" things. (I doubt this particular issue arises in the Swahili course, but I've seen it elsewhere.)