How can I solve "fatal error encountered during command execution" erro

fatal error encountered during command execution

private void btn_save_Click(object sender, EventArgs e)
{
    try
    {
        for (int i = 0; i < dataGridView1.Rows.Count; i++)
        {
            MySqlCommand cmd3 = new MySqlCommand();
            cmd3.Connection = con;

            cmd3.CommandText = "insert into sales-product(sales-id, product-name, qty, price, gross-total)values(@sales-id, @product-name, @qty, @price, @gross-total)";
            cmd3.Parameters.AddWithValue("@sales-id", lbl_invoice.Text);
            cmd3.Parameters.AddWithValue("@product-name", dataGridView1.Rows[i].Cells[2].Value);
            cmd3.Parameters.AddWithValue("@qty", dataGridView1.Rows[i].Cells[3].Value);
            cmd3.Parameters.AddWithValue("@price", dataGridView1.Rows[i].Cells[4].Value);
            cmd3.Parameters.AddWithValue("@gross-total", dataGridView1.Rows[i].Cells[5].Value);

            MySqlCommand cmd4 = new MySqlCommand();
            cmd4.Connection = con;

            cmd4.CommandText = "insert into sales(id, date, time, qty, gross-total)values(@id, @date, @time, @qty, @gross-total)";
            cmd4.Parameters.AddWithValue("@id", lbl_invoice.Text);
            cmd4.Parameters.AddWithValue("@date", lbl_date.Text);
            cmd4.Parameters.AddWithValue("@time", lbl_time.Text);
            cmd4.Parameters.AddWithValue("@qty", lbl_items.Text);
            cmd4.Parameters.AddWithValue("@gross-total", lbl_total.Text);

            con.Open();
            cmd3.ExecuteNonQuery();
            cmd4.ExecuteNonQuery();
            MessageBox.Show("Record Successfully Inserted !!");
            con.Close();
        }
    }

    catch (Exception ee)
    {
        MessageBox.Show(ee.Message, "Record Not Successfully Inserted !!");
    }
}