NSA was instructed by Obama and Lynch to record meaningful conversations of Americans which is illegal. But its another matter
Flynn's conversation with Russia got recorded.
Later, FBI investigated collusion and asked about Flynn's conversation, which is very unethical (asking a person for conversation Authority already knew)
Flynn told FBI what he said
FBI compared his verbal words with recording and found not match. He is charged lying
You can try it.
Let 1000 people talk with you and record their conversation.
In a just one hour, ask each one of them what he or she said.
I bet no one from these 1000 people can tell you verbatim word by word.
In legal sense, they lied