Can we create multiple delivery notes on an invoice as our clients in the trading business require multiple deliveries over time on the same invoice.

Thanks for posting to the Community, @karim2.

Currently, we're unable to create multiple delivery notes on an invoice for an invoice is a final sale.
 

I suggest creating an estimate for delivery notes since it is a non-posting entry until you combine it all together to the invoice.
 

When you create the invoice, the recommended estimates will appear to add it to the invoice.

Otherwise, you can print a packing slip and attach it to the delivery items.

Let me show you how:

1. Go to Sales and then choose Customers.
2. Select the customer's name to display a list of their transactions.
3. From the Transaction List tab, select the box next to each invoice.
4. Select the Batch actions drop-down, then choose Print packing slip.
    
5. The print preview screen will open so you can select printing options, preview, and print.
    

You can also check this article about how to email multiple sales forms: Email or print multiple invoices and sales forms.
 

Please let me know if you have additional questions. I'll be around to help. Take care!