What is wrong in my this backup code? sql C#

Hi
What is wrong in my this backup code it always not working and gives me an error

 SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;
                                     AttachDbFilename=D:\repos\mysales\WindowsFormsApp4\Database1.mdf;
                                     Integrated Security=True;
                                     ");
 string database = con.Database.ToString();
 if (textBox1.Text == "") 
 {
     MessageBox.Show("Please Enter Backup File Location");
 }
 else
 {
     string cmd = "BACKUP DATABASE [" + database +"] To DISK = '"+ textBox1 .Text + " \\ " +"database"+"-"+ DateTime .Now .ToString ("yyyy-MM-dd--HH-mm-ss") +".bak'";
     con.Open();
     SqlCommand  command=new SqlCommand(cmd, con);
     command.ExecuteNonQuery();
     MessageBox.Show("Database Backup Done Seccessfully.");
     con.Close();
     button2.Enabled = false;
 }