Login Failure while send message using WhatsApp api c# -

when i'm trying send message using c# api whatsapp # , handle onloginfailed event

and show me message of loginfailed

here's code

     wa.onconnectsuccess += () =>         {             messagebox.show("connected whatsapp...");              wa.onloginsuccess += (phonenumber, data) =>             {                 wa.sendmessage(to, mes);                 messagebox.show("message sent...");             };              wa.onloginfailed += (data) =>             {                 messagebox.show("login failed : {0}", data);             };              wa.login();         };          wa.onconnectfailed += (ex) =>         {             messagebox.show("connection failed...");         };          wa.connect();