It is not mandatory to use that code. Indeed not all sellers use an app which is needed here.
You cannot mark items paid and dispatched on the Classic view anymore, you need to do this from the Seller Hub.
https://www.ebay.co.uk/sh/ovw
Go to All Orders >> Awaiting Payment
Click on the square next to the item.
Use the 'More' drop down at the top of the page.
Mark as Payment Received.
Mark as Dispatched.
