This method is to get “Beach body wave curls,” a looser curl that falls down your back.
So instead of pointing the tip of the flatiron down, point it up, angling up (the angles do the curls).
Keep hair centered in the flatiron to avoid snags. Upon getting it all wound around the flat iron, carefully unwind. If the curl comes out too tight, you can run your fingers through it to loosen it up.