It's just finicky ... I got three of mine to register and it does work if you do things in a very methodical manner. But the reality us when we unlock our devices we don't do things methodically, and thereby using the finger print scanner quickly often retails in unrecognised attempts. Likewise the fact the pass code then requires a letter and digit combination means entering that after failed attempts is longer than it needs to be too. The whole point of unlocking your device should be quicker, sadly it isn't and neither is it any more secure than a pattern lock or PIN number. So yeah, as a convenient way to unlock your phone it fails big time ... As a Paypal payment method where you take your time it works well however.