return; return what?

And your code will fail with bigger values, read this again:

take the sum of the digits of n. If that value has more than one digit, continue reducing in this way until a single-digit number is produced.

spoiler flag, please.

I don't think it's possible :/ Because it's marked as spoiler, only those who solved it will be able to see it, so it's not a big deal. But discourse section is more for discussing issues or problems with code, description, etc. Just so you know for future :P

I'm sorry, i didn't know, how can i remove it?

Don't post your solutions in discourse! It's forbidden. Use the solutions tab.