Welcome to the community!
Hmm, if I understand this correctly, you’re trying to run C# in the code interpreter, did I get this right?
In that case, unfortunately, I’ve got bad-ish news for you. As far as I know, the code interpreter only works in python.
The good news is the model can generally readily translate C# into python, and then execute that. Have you tried that? Sometimes you just need to tell it.
Does that help?