> For the complete documentation index, see [llms.txt](https://docs.finpay.id/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.finpay.id/payment-gateway/integration-method/core-api-host-to-host.md).

# Core API (Host-to-Host)

## Overview

**Core API (Host-to-Host)** lets your system talk directly to Finpay Payment Gateway via API.

You keep the payment UI and data input inside your website or app. You do not redirect customers to a Finpay-hosted checkout page.

This model does not require you to store cardholder data. Card data should never be stored on your servers.

## When to use Core API

Use Core API when you need:

* Full control over checkout UI and UX.
* A single API integration across multiple payment channels.
* Deeper control over retries, reconciliation, and custom business logic.

Use [Hosted Payment](/payment-gateway/integration-method/hosted-payment.md) when you want the fastest go-live.

## Key integration concepts

### Authentication and access

Core API access depends on your merchant configuration.

Review the [Security](/security/overview.md) requirements early.

### Idempotency and retries

Network retries happen.

Design your integration to avoid duplicate charges and duplicate order creation.

{% hint style="warning" %}
If you are unsure how idempotency is implemented in your environment, align with Finpay before go-live.
{% endhint %}

## Supported payment channels

Channel availability depends on your merchant profile and configuration.

See [Payment Channels](/payment-gateway/payment-channels.md) for the current list and limits.


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