Thank you for the suggestion, I will leave it open as a feature request, if it’s something that is popular amongst other users we can definitely look into this further.
Just for others to trigger some potential interest. The additional notes could be set by default to have:
your preferred invoice format, e.g "Please send invoices to accounts@yourcompany.com in pdf format.
your payment terms, e.g. “unless otherwise agreed invoices are paid in 30 days”
you could request acknowledgment of the order
For us I’m keen to have a line in there stating “any client details passed to a supplier are to be used solely for the purposes of providing the service ordered and not for marketing or any other purpose”.