I did not receive an invoice for the purchase on SuperMemo.com

Invoices are issued after the purchase and are available for download after logging in to SuperMemo.com, usually within a few days from the purchase date (at the latest by the 15th day of the following month). To download an invoice, go to the “More” menu and then open the “Order history” tab. In this tab, for each order, there is an option to download the invoice.