I need a billing and sales system for our Voip Service

We are using a Fusionpbx (Freeswitch based system) to serve our customers with their VoIP telephony. Currently we need a system that can help us to sale and to bill to our customers. For this development, we prefer to be developed in Node JS, the database system use is Postgresql, we work in debian 10 and require that any development becomes our exclusive property and come well documented. These systems need to be connected to our VoIP platform.