Looks like typing the answer with the kanji (この時計は軽くないです) is wrong. I reported it.
Same problem here, still get wrong. Reported (16th jan 2019)
are you sure they are correct kanji?
So, tokei would be a clock in a home and not a watch?
I wrote, この時計は軽くないです and it was marked wrong, so did I use the wrong Kanji?
No, you didn't
It's just Duolingo, who doesn't accept kanji.
「この時計は軽くないです」is not accepted.
This sounds like something Flavor Flav would complain about.