# Overview ## Invoice Invoices are statements of amount owed by a user, and are either generated one-time, or generated periodically from a subscription. Standalone invoices contain items which are product prices that have a “one-time” frequency. You can also create a one-off product which will be a temporary product just for the sake of a particular invoice. ## Subscription Subscriptions allow you to charge a user on a recurring basis. Subscription creation requires items which are product prices that have a “recurring plan” frequency. Subscription will generate invoices according to the billing cycle (monthly, weekly, biweekly, annually). --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.zumrails.com/invoices-subscriptions/overview.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.