Prestashop: How to add the invoice number to the backoffice orders grid

Source: https://www.prestashop.com/forums/topic/300119-solved-how-to-add-the-invoice-number-to-the-orders-grid/?do=findComment&comment=1517949

Try to start with adding another array item to $this->fields_list

add code to:
/controllers/admin/AdminOrdersController.php

‘invoice_number’ => array(
‘title’ => $this->l(‘Rechnung-Nr: ‘),
‘width’ => 50
),