Hi danield68,
At our checkout page you need to fill the form with your data you would like to see on the invoice. After completing the checkout within 24 hours you will receive an email with your licence file attached. The licence will be available at your "My Licences" page too ( https://sketchucation.com/webshop/my-licences.php ). From the My Licences page you can download / print your invoice which you can use as a proof of payment.
In case you need any other type of proof, please connect or support at support[at]sketchucation.com email address.