Got quite stumped by the 1st challenge ( 6 characters). Somehow it does not let me use more than one number in that level. First try was 123456 but even qwer12 was not accepted.
Once I got past that level, the game started to click and the challenge was to create as easy a password to comply with the requirements.
The instructions screen both disappears too fast (at first playthrough) and not fast enough (2nd playthrough). This could have used a button to skip the text and go straight into the game as well as a button to acknowledge that the player is done with reading.
Overall I had fun coming up with the passwords, 123!@Qwertyu out !