billing date question

[sokalsondha]

hello members.

happy new year. i came up today with a very important question.

i am using whmcs for my ISP. currently only selling broadband to residential customer. so i put in automation >>billing settinggs ..14 days.

which is working perfect no problem

i am going to add a phone service with the broadband too. so the broadband and phone bill will be together in one invoice.

so for example customer billing start at 8th of August. so as per current system its generate invoice on 26th of July which is 14 days

but when i will be start the phone service i need to generate the invoice on the same day service expired because i need to add the phone usage bill from the previous month

so plan is customer will get the invoice on 8th of the August even its his date expired. and he have 7 days to make payment of the bill. and if he dont pay within 7 days his service will be suspended on the 8th of the day

so what value i should put instead of 14 days in the automation settings? 0 ?

because i want he get the email invoice the day his line going to be expire

i can't do any test as its on live sytem

so please someone help me with guide

 

thanks a million