You don’t need this, as there is a two click option already available in the Sales App:

The benefit of this approach it is also gives you the ability to Invoice Orders where time has been ‘delivered’ and/or where fixed price products were sold and can be Invoiced.

Note: This approach is a proof of concept that may need to be modified. Contact your Odoo Digital Advisor or Odoo Partner if you don’t have the skills to implement this. For databases implemented by Odoo, this will generate line of code maintenance charges so we can support and upgrade this feature in future versions.

An Automation Rule can be created like this:

Code:

for record in records:
    sale_order = record.sale_id
    
    if sale_order and sale_order.invoice_status == 'to invoice':
        invoices = sale_order._create_invoices()
        
        if invoices:
            msg = f"Invoice automatically generated upon delivery"
        
            record.message_post(body=msg)
            sale_order.message_post(body=msg)

When the Delivery Order is validated:

1) The Delivery Order chatter shows:

2) The Sales Order chatter shows:

3) A Draft Invoice is automatically generated