Columncount property cannot be set on a data-bound datagridview control

var dt = new DataTable();

            dataGridView1.ColumnCount = 2;
            if (checkedListBoxKategori.Text == "Kundnr")
            {
                const string constring = @"Data Source = MARTIN; Initial Catalog = FakturaDB;Integrated Security = True";
                using (var con = new SqlConnection(constring))
                {
                    using (var cmd = new SqlCommand("SELECT * FROM FakturaDb", con))
                    {
                        cmd.CommandType = CommandType.Text;
                        using (var sda = new SqlDataAdapter(cmd))
                        {
                           
                                sda.Fill(dt);

                                //Set AutoGenerateColumns False
                                dataGridView1.AutoGenerateColumns = false;

                                //Set Columns Count
                              
                                dataGridView1.ReadOnly = true;

                                //Add Columns
                                dataGridView1.Columns[0].Name = "Kundnr";
                                dataGridView1.Columns[0].HeaderText = "Kundnr";
                                dataGridView1.Columns[0].DataPropertyName = "Kundnr_ID";
                                
                            }
                        }
                    }
                }
            
            else if (checkedListBoxKategori.Text == "Namn")
            {
                const string constring = @"Data Source = MARTIN; Initial Catalog = FakturaDB;Integrated Security = True";
                using (var con = new SqlConnection(constring))
                {
                    using (var cmd = new SqlCommand("SELECT * FROM FakturaDb", con))
                    {
                        cmd.CommandType = CommandType.Text;
                        using (var sda = new SqlDataAdapter(cmd))
                        {
                            
                                sda.Fill(dt);

                                //Set AutoGenerateColumns False
                                dataGridView1.AutoGenerateColumns = false;

                                //Set Columns Count
                                
                                dataGridView1.ReadOnly = true;

                                //Add Columns
                                dataGridView1.Columns[1].Name = "Namn";
                                dataGridView1.Columns[1].HeaderText = "Namn";
                                dataGridView1.Columns[1].DataPropertyName = "ForNamn";
                                
                            }
                        }
                    }
                }
            dataGridView1.DataSource = dt;
            }