Welcome back, warren6.
The settlement discount can only be added by the time your customer has paid the invoice. Thus, the need to go back to each transaction and adjust the amount.
I can see how easier it would be if only you can apply it at once.
Just in case you want to personalise your sales forms, here's an article you can read for the detailed steps and information: Customise invoices, quotes, and sales receipts in QuickBooks Online.
Please know that you can visit our Community forum again if you have other concerns with QuickBooks Online.
