> ## Documentation Index
> Fetch the complete documentation index at: https://developers.fd.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# Custom Integrations

> No official plugin for your platform? Make any store agent-payable with the same open protocols and APIs our extensions are built on.

Our [official extensions](/prism/platforms) are convenience layers over open protocols — nothing about agent commerce is locked to a specific platform. If you run a custom storefront, a headless build, or a platform we don't yet cover, you can add agent payments yourself with the same APIs, and you'll be in production quickly.

There are three ways in, depending on how much you want to build.

## 1. Follow the merchant integration pattern

Every official extension implements the same three-step contract, and you can implement it directly against any stack. Your server needs three things — a discovery endpoint, a checkout call, and a settle call. Prism handles all the token math, chain selection, and x402 formatting.

<Steps>
  <Step title="Advertise the handler">
    Expose a `/.well-known/ucp` profile that includes the Prism payment handler
    (`xyz.fd.prism_payment`), fetched from your Prism account.
  </Step>

  <Step title="Prepare checkout">
    When an agent starts a checkout, call Prism to get the x402 payment
    requirements for that order and return them in your checkout response.
  </Step>

  <Step title="Settle on-chain">
    On completion, forward the agent's signed payment credential to Prism's
    settlement endpoint. Prism settles on-chain and returns a confirmed
    transaction.
  </Step>
</Steps>

<Card title="Merchant integration guide" icon="store" href="/prism/integrations/ucp/merchants">
  The full three-endpoint walkthrough — request/response shapes, token base
  units, and settlement — the exact pattern our official extensions follow.
</Card>

## 2. Drop in a server-side SDK

If your backend is in TypeScript, Python, or Java, the Prism SDKs handle authentication, request signing, and payment verification for you — often just a few lines of middleware on the route you want to protect.

<CardGroup cols={2}>
  <Card title="SDK overview" icon="code" href="/prism/sdk/overview">
    Framework guides for Express, NestJS, Next.js, Fastify, and the base
    language SDKs.
  </Card>

  <Card title="API reference" icon="square-terminal" href="/prism/api-reference/introduction">
    The Prism Gateway REST API, if you'd rather integrate without an SDK.
  </Card>
</CardGroup>

## 3. Bring your own payment handler

Prefer to keep your existing commerce protocol layer and only add settlement? Each official extension exposes a **pluggable payment-handler interface** — you can ship your own settlement provider as a standalone package that self-registers, without forking the core plugin. The same interface is what our Prism and dummy/test handlers are built on, so there's a working reference to model yours on in each repository.

## Understand the protocols first

If you're new to how agents discover and buy, start with the concepts — the standards are what make any of these paths interoperable.

<Card title="Commerce protocols" icon="diagram-project" href="/prism/concepts/commerce-protocols">
  UCP, ACP, and x402 — how AI agents discover a store, build a checkout, and pay.
</Card>

<Note>
  Building an integration for a platform we don't cover yet? We'd love to hear
  about it — [get in touch](https://fd.xyz/contact-form).
</Note>