1. Find the "Sales" button on the left side of the screen. Choose the "Invoices" button and click on it.
OR
1. Find "Traders" on the left side of the settings panel. Find the user, type on "Person View".
2. Find on the left side the "Invoices" button and press it.
Common next steps for both ways above
1. Choose a particular invoice and as it opens, find a button "More" on the right side of the screen and click on it.
2. Choose "Copy Invoice" in the falling list.