Flynn was in a casual conversation with two FBI agents who he somewhat informally invited to his then-White House office, and even gave them a friendly office tour.

Flynn committed no crimes. He was charged with perjury regarding discussion of a conversation with the Russian ambassador Flynn was legally allowed to have. The only crime was the manufactured perjury. And even the two FBI agents who manufactured the perjury said that Flynn appeared to be not be lying, or at least unaware that anything he said was untruthful.
It is a manufactured "process crime", not an actual crime, used to extort Flynn to either "sing" or "compose" something incriminating about Trump. And Jerome Corsi in the last week said the Meueller team gave Corsi a scripted lie to testify to, and he would rather spend the rest of his life in jail than take the offered plea deal to lie. The partisan Mueller investigation is a house of cards, ready to collaapse.

Tucker Carlson had an exceptional overview of the manufactured case against Flynn last night (Friday, Dec 14, 2018)
https://www.youtube.com/watch?v=fVGLPpiYqcM