Systems and methods for invoking functions to cause a change in a displayed price provided for output in a third party website, comprising receiving data corresponding to one or more codes each associated with a respective promotion. In response to determining that a webpage of the third party website output in a web browser is associated with initiating a payment process with the third party website, an interface element is generated and presented in another interface of the web browser. When a user selection of the interface element is received, each of the codes is applied to a data entry interface in the webpage, and based on the respective outcomes of applying each of the codes, a particular code that results in a greatest change in the displayed price is identified. The particular code is then applied to obtain a resulting price that is displayed in the webpage.