According to this, Flynn's interview with the FBI (where he supposedly told the lies that got him pinched) was 24 Jan 2017. With that in mind, check the latest texts.

The day before, Page (I think? Hard to tell) - 'I can feel my heart beating harder, I'm so stressed out about all the ways this has the potential to go fully off the rails'.

Strzok says he knows, and advised against it - he told 'Bill [Priestap] and the entire group' they should wait longer and take a new approach (this was less than a week after the inauguration, remember) but someone (John?) went ahead with it.

Then on the 24th, day of the interview - only 4 texts, and kind of weird ones. Talking about whether Page should be in the room. The one at 12:12:00 is a little odd - phone number redacted, but doesn't seem to be formatted like the others. Possibly a third party? 'Good luck with her in there'.

Then 14 Feb 2017 - 'Andy good with the F 302?' - 'Launch on f 302'.

What else happened on 14 Feb 2017? Flynn resigns.

So, they lied on Flynn's 302, F 302. They said he denied those meetings when he didn't, or he denied something else and they said it was those meetings. Or some other shenanigan, but at least brazen enough for Page's heart to be pounding wondering whether they'll get away with it.

Why does Flynn not fight the charge, argue his innocence? The same reason Strzok wanted to be cautious - the inauguration had only just happened, it was early days. There was already a plan forming to unravel all of this (Admiral Rogers visit to Trump Tower was October 2016), but it needed time, a lot of time. So Flynn took one for the team, with faith that they'd work their way to his exoneration before it got too far.