To create invoices from a single sale order containing the products and quantities in the pickings related to the order, you need to:

* Click on the "Create Invoice" button in the sale order.

* Select "Regular Invoice" as the invoicing mode.

* Select the pickings whose products and quantities need to be invoiced. If no pickings are selected, the process follows the regular flow.

To create invoices from multiple sale orders containing products and quantities in the pickings related to those orders, you need to:

* Select the sale orders from the sale order tree view.

* Click on Action > Create Invoices

* Select the pickings whose products and quantities need to be invoiced. The invoices are grouped when possible. If no pickings are selected, the process follows the regular flow.

To invoice the products and quantities in the pickings related to the orders and also invoice the service products from the sales orders (if any), check the 'Invoice Service Products' checkbox. 

In addition, you will notice that if there is any sale of the selected pickings that contains any uninvoiced service products, a message will appear confirming this fact and the 
'Invoice Service Products' checkbox will be checked by default, but it is editable.  

The field "Invoiced" in the "Additional Info" tab in pickings shows whether the products in the stock picking have been invoiced. This field is automatically updated. However, it can manually be set to True or False. Only pickings with the field set to False can be selected in the invoicing Wizard.
