(RADIATOR) Simple Question

[Philip Buckley]

Hi there,                       I am using Radiator 2.13 and Rodopi billing system and I want to set up a system where I can give a user a fix amount of hours then has the user log off the hours are decrement until the users have no hours left and are not allowed to log on. This is similar to the 100 free hour that AOL has. Has anybody implemented this system or knows how to do it even if it is not with Rodopi billing system.