I dont think you can add a functions name to the context, only files (with optional line numbers). You can try selecting the method body in code, copy, and pasting it into the chat, or select the method body and press Ctrl+K (or MacOS equivalent). This will add the lines of code and file to the context. Then you can refer to it in the request.
Really, that is weird. Maybe try going back to a version and see if it works there. I have never noticed this feature and would be surprised it exists because it would have to have all these methods indexed or something.