"He told the truth at the interview."
Translation:Είπε την αλήθεια στην συνέντευξη.
I have the same question. Στην seems incorrect to me because the following word doesn't start with any of the words that require the ν. Hopefully a native Greek speaker will comment with the answer.
Στην is recommended to become στη if the following word does not start with a vowel or κ,π,τ,ψ,ξ,γγ,γκ,μπ,ντ,τζ,τσ. That is recommended, but you can keep the -ν if you want.