Hyvää päivä is wrong?
It would need to be "hyvää päivää" (in the partitive case) to be correct. If you wrote it that way and it was not accepted, you should report it.
shouldn't kauppatori be an acceptable translation for market square?
Should't " Päivää, tuolla on lähin tori " be accepted ?
It is okay, but if we are very literal, that would be 'good day, there is the closest market square' in English too
the closest market square is over there: 7 words, 33 letters
lähin tori on tuolla: 4 words, 17 letters
compact and efficient, like finnish design
Why adding market before square ?