Translation:A cup of coffee and a piece of cake, please.
They will likely come to accept it after reporting. Why it hasn't been accepted by default is probably due to piece translating to pala whereas slice would be viipale in Finnish. And here we usually say pala kakkua/ kakkupala, although it wouldn't be wrong to ask for a viipale kakkua/ kakkuviipale (it's just uncommon).
Huh. So, how would you specify that you wanted just one piece? I understand that you can use kakkua for "some cake," but what if you wanted to be less vague about the portion of cake? Is there some sort of counter for Kakku like there is for a piece or slice of cake in English?
But in another place in the course there was “miljoona” translated as “one million” and not “a million” justified by it meaning the same thing (both would work grammatically in English). In theory “a cup of coffee” is the same as “one cup of coffee” too. :) There are some inconsistencies like that in the course. Hopefully they will get fixed over time.
I'm not talking about Finnish here, don't know it enough, but in terms of English it is the same- a million is one million, not two million, it doesn't HAVE to be translated as ONE million. And a cup of coffee also can't mean two cups of coffee. Just pointing out the inconsistency in translation into English, not the Finnish side of it.