In order to generate the backups required for Accounts Receivable, you need to download all of the invoices for internal orders for the month.
This is easy to do.
Go to Stitch Labs. Click on the Orders tab.
Click on Channels and select Stitch.
Click on All to show all orders (not just Open ones).
At the top, select the first and last date of the month you want to pull the backups for.
You should see all of the internal orders for that month. Click on the checkbox next to the ID column to select all internal orders.
Click on Bulk Actions > Download Invoices. This will download all invoices for the month into one PDF. These are your backups for the month.
Note about refund
If there are any refunds in these invoices, you have to also capture them. They do not download with the invoices.
There is a tab on each order that says "Refund", which is activated if there has been a refund.
There's no easy way to capture these beyond a screen capture. (CMD-SHIFT-4 on a Mac, Print Screen on a PC).