SqlBulkCopy Tutorial SqlBulkCopy - The DestinationTableName property must be set before calling this method.

// Oops! The destination name is empty
string destinationName = "";

using(var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServer()))
{
    connection.Open();
    using (var sqlBulk = new SqlBulkCopy(connection))
    {
        sqlBulk.DestinationTableName = destinationName;
        sqlBulk.WriteToServer(dt);
    }
}

string destinationName = "Customers";

using(var connection = new SqlConnection(FiddleHelper.GetConnectionStringSqlServer()))
{
    connection.Open();
    using (var sqlBulk = new SqlBulkCopy(connection))
    {
        sqlBulk.DestinationTableName = destinationName;
        sqlBulk.WriteToServer(dt);
    }
}