An online system receives an advertisement (“ad”) request identifying an application, one or more items for use within the application, ad content, and a prompt for purchasing one or more of the items. The prompt for purchasing an item comprises text or image data describing the purchasing and instructions that, when executed by a client device, request payment information from a user accessing the prompt. When the ad content is presented to a user, the prompt is also presented. When the user interacts with the prompt, payment information is requested and communicated to a third party system associated with the application. The ad content and prompt may be presented to the user within a feed of content items provided to the user by the online system.