I have been operating on WHMCS + Freeradius unfortunately your system has more features. Am looking at a scenario i do recurrent billing. By default i would like to generate the invoice on 24th of every month for the next month cycle, 6 days to 1st of the month. I want also to send a payment reminder to the client on 28th before 1st of the month. Same to prepaid i want to send the client an early notice (No invoce here) that their service will expire in a few days time and they should pay before that day.