Sei di luglio
The question was to translate "Are you born in the month of July?" And the correct was "Sei di luglio". But i thought that translated to 6th July. My answer, which was rejected, was "Sei nato nel messe di luglio". Why was that wrong?
It's "mese," not "messe," but other than that it looks correct. Maybe not the most concise way to say it, as compared to "sei di luglio" or "sei nato a luglio," but the English is pretty awkward as well. I guess the issue is that we don't say, "I am from July," but rather, "I was born in July," so they had to use "born."
The right translation of "are you born in the month of July" is "Sei nato nel mese di luglio?" or, better, "Sei nato a luglio?"
Summing up and adding my two cents. 'sei di luglio' translates both way - as you correctly pointed out, it also means 6th July. "Are you born in the month of July?" literally translates "Sei nato nel mese di luglio?" ('mese' with a single 's', that's why it was rejected I suppose). "Are you born in July?" translates to "Sei nato a luglio?" or "Sei nato in luglio?" (both are equivalent)