Where are my invoices, and how do I change my card?

Both are in Billing. Your receipts are listed under Receipts with the date, amount, tax and status; click View to open one in Stripe, where you can download or print it.

To change your card, click Update card. It opens Stripe's secure page, where you add the new card; Billing then shows it as the card on file. If a payment is overdue, the button reads Update card and pay.