So I've tried with most of my fingers, and both my thumbs. It doesn't work for me. (hopefully yet)
Most video tutorials/demo online just repeatedly tap the home button, and the red fills up the fingerprint onscreen. They tap when the phone vibrates while my doesn't vibrate and simply tells me to lift and then place again.
I don't see what I'm doing wrong, here's a video of my action, if someone can spot what I did wrong, please post it as an answer.
It's quite frustrating really.
Link to video: https://www.youtube.com/watch?v=F3VM4RcQu1A