Addon for existing billing system

Hello, I need a person who can implement an hlr api request to existing billing system. The client will type a phone number and get an answer from an hlr provider. The task is to online charge the client with a fixed amount per request. We will provide a ready made api request and the only thing needed is to implement it to the billing and charge the user from his existing balance. We will provide only access to a test server with the demo but fully functional version of the billing installed. We will the freelancer to give us everything changed and added so we can move it to our main server. No access will be given to the main server. More info upon bids.