MiniJson unity Android

Hello,

my application is about connecting to facebook getting the id and username.
i m connecting to Facebook Unity SDK and i can display the UserId in a guiText

now for the username i saw this expample:

so in my script i add this

using Facebook.MiniJSON;
    
    public GUIText DebugText;
    
    void FbUsername()
    {
       var dict = Json.Deserialize(jsonString) as Dictionary<string, object>;

       string userName = dict["name"];
    }
    
    void OnGUI()
    {
    DebugText.text = " Fb Username"+username;
    }

but it tells me jsonString does not exist in the current context.
What’s the problem

Thanks for your help

Here is the answer of this question: