"tamta zupa" is Nominative, so it is used mostly for the subject of the sentence. This here is not even a sentence, so by default it uses Nominative.
"tamtą zupę" is Accusative, used for the direct object. Like in "We are eating that soup" = "Jemy tamtą zupę".
So... your native Serbian is a Slavic language, doesn't it have cases? How would you say "That soup is tasty" and "We are eating that soup"?