First of all, great job on getting all of these web hosting advertisement spammers' attention with the title
Originally Posted by easyhostmedia
simple get WHMCS as your client/billing system.
WHMCS isn't the ultimate choice. There are other billing/content management systems that are just as good and cheaper - Biesta, BoxBilling just to name a few.
But essentially, yeah. These softwares are the easiest methods to solve your issue. The other way would be to develop it on your own