about session in c# .net

Question

hello friends

 

i'am working on e-commerce site i have facing a problem to store session value

 

when client click conform then client go to pay pal website and then complete payment and return to given page

 

i will get transaction id  

 

but in this page i will call session like:

 

if (Convert.ToString(Session["login_nm"]) != null && Convert.ToString(Session["login_nm"]) != "")

{

lbl_name.Text = (Session["login_nm"]).ToString();

lbl_msg.Text = "Thank You for shoping with us.";

}

 

 

and Session["login_nm"]) value store when client fill there details 

 

 but  Session["login_nm"]) this is empty

 

how get this value