Abstract: Methods, systems, a computer program and a computer program product for providing service authorization to a Charging Client function which comprises associating one or more charging modifier actions with a user account, each charging modifier actions having an action start time and defining a charging modifier parameter and receiving a service authorization request indicating a request for service reservation from a charging client. A validity time period for the service reservation is determined; one or more of the associated charging modifier actions having the action start time within the determined validity time period is identified; the identified one or more associated charging modifier actions are executed to activate the charging modifiers for the user account and a service authorization response indicating a service reservation to the charging client is sent, the service reservation based on at least one of the activated charging modifiers.