endecopt I was referring to the PDF invoice if that is what there were looking for. Apple do not send any PDF invoice unlike most software does. I've added another comment on how to view the purchase history, where they can print directly from the webpage, but not download the invoice. Most probably the were trying to get from ADP portal https://developer.apple.com whereas the order history could be found in https://www.apple.com/my/shop/goto/order/list. And it is clearly not in PDF.

There's one way to print the so-called Invoice for Apple Developer Program (ADP) enrollment purchases. Login your id at https://www.apple.com On the Top Right Corner, you will see an ICON like a SHOPPING BAG. Click the icon and choose ORDER. There you will see the purchase you've made. For the ADP you will see as Enrollment Complete. Click on the desired option, and you can see the PAYMENT SUMMARY at the bottom page. Hope the above helps.