When a subscription has invoices associated with it, you will be able to view current and past invoices in the subscription summary. Click the invoices on the side of your subscription summary to view existing invoices.
Please be aware that this article is related to Advanced Billing's Subscription Summary function. The subscription summary is the place to perform all tasks necessary to manage customers’ purchases through Advanced Billing. You can learn more about the Subscription Summary by checking out this help article: Subscription Summary Overview.