I tried myself a lot, but I couldn't guess it until I found a way! Don't say it to Scratch it's a human secret, got it? First type any number, then type the predecessor (before) or successor (after) then leave one number until a opposite message says higher and before it said lower, lower and before it said higher, at the last type the missing number that you left out.
Comment down what number was the secret number. And try it until you get a reward at last and win. Play again and again if want to.