If you selected "I want an invoice" when making the payment, this can be found in the link "My account → my purchases" that is displayed when you click on your name (at the top right of the screen).

If you have activated the automatic renewal of a subscription, simply fill in the tax identification number field (CIF, RUT, RFC, CUIT, etc. depending on the country) in your user account so that the invoices are also generated automatically.