AWS generates Usage, Subscription, and Refund invoices (a.k.a. Credit Memos) to provide you with a comprehensive invoicing experience. You receive AWS invoices monthly for usage charges and recurring fees. You may see an Out-of-Cycle (OCB) invoice for certain usage charges not included in your monthly usage invoices. For one-time fees, such as fees for purchasing an All Upfront Reserved Instance, you will receive subscription invoices for which you are charged immediately. Refunds/Credit Memos indicate any approved refunds granted to your account, which offsets the previously issued invoice.