You can download your own Content Sparks invoices anytime you need to.
Simply log into your Content Sparks account and head to the 'Orders' section.
From the list of your orders, you will see an 'invoice' button on the right hand side of each one.
Click this button and your invoice will automatically download in .pdf format for you.
Look out for the pop-up blocker on your browser which may interfer with the download process.