paid item; in-app purchase; microtransaction item (e.g. in a video game)
spending excessively on in-game items
not paying for virtual goods or premium features (in a video game, on a social networking service, etc.); free-to-play player; F2P player
spending heavily on virtual goods or premium features (in a video game, on a social networking service, etc.)
charging for in-game items; microtransaction
fee-based system; billing system
billing information; accounting information