You can find and download past invoices in the Account Settings menu.
Step by step:
On a computer, log into your account.
In the top-right corner, click the account menu.
Click Account Settings.
On the left, click Subscription.
Click Manage Subscription and Billing.
A new page opens on Stripe.com, Riverside's payment processor.
Under Invoice History, click the billing date to download that invoice.
Click View More to see older invoices. Contact support to access invoices from more than a year ago.