It's normal that you don't see any traffic using Charles, since Charles can only intercept traffic made by HttpUrlConnection or OkHttp, since flutter is not using any of those two..you can't see anything in Charles.
on page 397 there is entry in index:
iWalk, v2 71
on the same page there are interesting terms like
islamic terrorism, jihad via internet, judism...
also page number 71 which stands next to iWalk term is interesting coincidence since this riddle is celebrating 71 years of Israel independence...