flattened=flattened.reindex(['invoice_id','reservation_id','Usage_gross',

                             'Mileage_gross','Late_return_gross',

                             'PCN_gross','PCN_admin_gross',

                             'Flex_gross',

                             'Driving_credits_gross',

                             'Total_VAT'], axis=1)

flattened=flattened.fillna(0)