# Introduction

## Purpose

This document provides requirements specification of Web Service API at Biller Gateway.

## System Architecture

The system architecture overview that illustrate and example of the overall sysem, the connectivity and interaction with each other, is depicted in the diagram below:

![](/files/9EfiVRJ1eytRwVTFYtLe)

1. Client did payment or prepaid reload transaction through client channel (e.g. Internet banking, EDC, ATM, Mobile payment, etc). The request will be sent to the switching.
2. Switching forward the request to the core banking/E-Money in order to debit customer accounts as a nominal amount of transactions conducted.
3. Core Banking/E-Money will send a response to switching once debiting process is completed.
4. After getting the response from the core banking, switching will proceed the request (purchase or payment) to biller GW.
5. Biller GW forwards the request to aggregators or billers, furthermore that response will send back to Switching.

{% content-ref url="/pages/EsMLTykQ1iXdf0BcDL9c" %}
[Functional Requirements](/biller-gateway/reference/functional-requirements.md)
{% endcontent-ref %}


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