The demo is limited to levels up to 7. One reason is that I find levels a bit higher than 7 often quite difficult (if the move limit is turned on), which can feel quite frustrating, and that's not really the experience the demo should provide. An unfortunate effect is that some players (if they are particularly bright or just unlucky) might play through the demo without experiencing any challenge. Therefore, I decided to find and share three puzzles on level 7 that I personally find more difficult than the average puzzle on level 7.
I came up with these codes: 1861-07, 4736-07, and 9962-07.
To play these puzzles in the demo, you first have to unlock level 7 by solving puzzles on levels 1 to 6. Then you start a game with NEW GAME (in the main menu) and select CODE instead of a level to enter one of the codes. (Make sure that MOVE LIMIT is turned ON in the SETTINGS.)
Enjoy and please let me know what you think of the difficulty of these puzzles!