JSON API to integrate to WordPRess

The VOIP suppliers have an API for working with their numbers - buying a number, choosing a number, statistics by number, price for numbers and prices for calls… .: [login to view URL] (version 3). There is also an SDK for this API: [login to view URL] To work with suppliers, we need a new billing plugin for WordPress on our side, which will process data from the server using the API. The main point is as follows. For the supplier, we are a single customer reseller. We have numbers and balance in our account. The task of the billing plug-in is to break down calls and numbers by clients, maintain their individual balances, separate statistics on calls and call costs, payment methods from clients - i.e. completely all breakdown by individual clients. Plus the ability to set a price for your reseller on top of the one that the supplier gives us. This plugin will have admin access for managing clients and access for end clients: client profile, client numbers, statistics, balance, etc. Please see the detailed technical requirement.