Nothing particularly wrong, but this course doesn't accept it.
I'd say this were a political decision (some people think that Kiev is transliterated from Russian and Kyiv is transliterated from Ukrainian; even though Ukrainian oblique case stem is, funnily, Києв-, so Kiev could be a transliteration from Ukrainian too xD), but this course sometimes doesn't accept other perfectly correct variants so this might be just a bad course design. Let's hope the Ukrainian team will add more variants in the future.
Sorry, the UkrDuo administrators decided not to accept "Kiev". My opinion is that it's the common spelling of Київ in other languages, that politics has no place on Duo, and that forcing Duolingo learners to spell Kyiv will not change their attitude to Ukraine, same as allowing them to spell Kiev :)
But I'm not the one who decides :')
'Kyiv' is the default spelling in this course, what's your problem?
'Kiev', however, is a widely-used alternative, and I believe it should be accepted, too.
Looks like the audio was cropped here, that's why it sounds strange.
Sorry, as I wrote in a comment above, the administrators of this course decided not to accept "Kiev".
I agree with accepting "Kiev". It's the most common official spelling in English. People spell it that way not because they don't think Ukraine is an independent country, or that Ukrainian is a language different from Russian, but because it's just the spelling. We also spell "Rome" and not "Roma". Yes, this spelling comes from the Russian word "Киев". But. It used to be spelled as "Кыѥвъ", so there is indeed connection with "Kiev" which is deeper than just the Russian language. Also, since nobody knows how to pronounce "y" and since short "i" in English sounds quite similar to "и", spelling it as "Kiev" makes sense. Yes, there is #KyivNotKiev. And yes, several countries have already made it their official spelling. And some media are using it in support of the campaign. However, that does NOT yet make "Kiev" wrong. Especially if we're talking language and NOT politics.
However, it's up to a few people who are in charge of the course to decide :) They want to support the "Kyiv" movement, and they decided that the users have to follow this too. There are good sides to this too, like raising awareness about the "Kyiv" spelling. But I think making "Kyiv" the default, but still accepting "Kiev" would have sufficed, people should have a choice, and a right to use an officially correct spelling in a language course.
Slightly different point than the correct English spelling of Kyiv, but can I ask why Киеві isn't accepted? On the earlier courses it swaps between requiring Київ and Киевї.
The Kyiv city website seems to use Киеві (https://kyivcity.gov.ua/news/vitaliy_klichko_sogodni_v_kiyevi_ifa-testuvannya_mozhut_robiti_12_zakladiv_okhoroni_zdorovya/) ok, but this course seems to change its mind without reason.