To download your invoice, you will need to navigate to your Purchases page, on your PSEngine account. To do this you will need to visit www.psengine.co.uk. Once there you may need to log in:
When you are logged in, or if you are already logged in, you need to click on Account > Purchases:
Once on the Purchases page, the Download Invoice button will be next to your View Licences.
Your invoice will be provided in PDF format.