Specifically, Flynn asked Russia to delay a vote condemning Israel for settlements, and to not “escalate” after the Obama administration imposed lame-duck sanctions on Russia (efforts by the Obama administration to torpedo relationships with foreign powers, to make it harder for Trump to work with them). Obama prosecutors claim that Flynn was “conspiring” with the Russians, even though it had nothing to do with collusion during the election (since it was after the election was over).
We shouldn't know the details of the conversation, but Flynn had been illegally wiretapped because of the funded-by-Hillary-Campaign fake pee-pee dossier, that the Obama cronies had used as an excuse to tap Flynn's phone. And Flynn’s identity was illegally unmasked and illegally leaked to the public, all crimes and abuses of power to undermine the U.S. interests.
So there's some crimes here a lot more serious than the never enforced Logan Act, but it's by the Obama administration. Yet, somehow this never gets mentioned by the Press when talking about Flynn's high crime of lying to the FBI about what he talked about, to un-fuck a relationship that Obama was trying to sabotage during his last days in office.