Translation:It is hot tea.
Kind of wish they'd stop forcing us to guess the nonexistent subject. I put in "hot tea" because I had a feeling "The tea is hot" would be wrong. Turns out, both are wrong. The mysterious subject that isn't there is not "the", but "it". Silly me, how would I not know of the specific nonexistent subject Duo wants?
”hot tea" would be "atsui ocha"
when you see "desu", you know that it is some variation of the word "is". So what does this sentence mean? "Is hot tea" does not make sense in english, so you put in the only logical thing "it is hot tea", which is accepted.
I got it wrong too, because I put in "it's a hot tea" which is apparently bad english (not a native english speaker).
I've heard "a hot tea" used informally in English. For example, if someone offers you a drink: "I'd love a hot tea." Or "I love a hot tea on a cold winter morning." Similar to what hollt693 says, it's shorthand for "a cup of hot tea".
I can see how it wouldn't work as a translation for あついおちゃです though.
Where do you miss it?
You could say 「おちゃがあついです」 But then the meaning is slightly different － "The tea is hot".
You can directly clump together an adjective 「あつい」and a noun「おちゃ」。
Just like in english, then the adjective directly modifies the noun. "red car" "hot tea" "cute girl" 「あかいくるま」「あついおちゃ」「かわいい女の子」