How do we add notes to buyers when they check out?

[56bits]

I know there used to be a way to add instructions to buyers when they checked out, but I can't find the option for this in the new dashboard.

Just want to add a note ensuring that they include business name if it's sent to a commercial address, as this has been causing issues recently.

[designers*n*more]

When the item has sold, use the “send Invoice”  from the drop down menu for the item on the Orders page. You can add instructions in the box at the bottom of the page.

[eol-products]

That was my first thought but does not work once someone has already paid. I think the only solution is the add it into the description as I cannot find where you could change the buyer email.