Your C# "tokenize" method is a mess. For some unknown reason it adds closing parenthese ")" to the end of the input. Also, the regex is a complete mess too, it does not parse numbers at all and there are other issues with it.

Why even have such starting code if it is wrong?

That's precisely what an 8 kyu kata is for. It is pretty much just for people trying to learn the language.

I think this kata is too easy even for 8 kuy kata.