Unlike other billing systems like AWBS or WHMCS that have unlimited users, eJadSPM has 2 components to it, The base system (either professionl or enterprise) which you have to pay every year, and then a CAL or Client Access License for every customer that you invoice. This CAL can be leased, or you can BUY a one time perpetual license and never have to pay this fee again. This assumes you have one of their currently supported Control Panels like Plesk or Helm 4.

In addition to the fees above you can buy other 'extensions' if you want to do things like Exchange Hosting and if doing Exchange hosting then you also have to by a MAL or Mail Access License.