Congratulations on solving, but please don't post "spoilers" in Discourse - although admittedly you are not specifically giving a coding solution, it is giving a big hint to finding a correct approach to solving.

There are already lots of partial hints and detailed troubleshooting advice in the various replies below, if people are stuck they can make the small effort to read through such replies which cover 99% of the usual mistakes.

Especially on 4 kyu + katas, where users are supposed to have to use their own brains a bit to solve them.