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

# Payment protocols

> Choosing between x402 and MPP for agentic HTTP payments.

## What problem do these solve?

Both protocols let an agent or script pay for an HTTP-gated resource — an API call, a tool invocation, a dataset — with no human in the loop. A client requests a resource, gets `402 Payment Required`, signs a **payment credential** — a self-contained, signed payment authorization (the x402 spec's "payment-as-credential"; read it as *signed payment*, not a login credential) — and retries. Atum settles both the same way underneath, and neither Atum nor your server ever holds the payer's funds or keys.

The difference between them is architectural: **who verifies and settles the payment.**

## Which one do you need?

Match whatever protocol the other side of the payment already speaks:

* **Paying** for a resource? Use the protocol its `402` response speaks.
* **Gating** a resource? Use the protocol the clients or agents you want to serve already speak.

Building something new with no existing counterparty to match? Use the trade-off below.

## Facilitated (x402) vs. Direct (MPP)

|                          | [Facilitated payments (x402)](/payment-protocols/x402/overview) | [Direct payments (MPP)](/payment-protocols/mpp/overview) |
| ------------------------ | --------------------------------------------------------------- | -------------------------------------------------------- |
| Verifies and settles     | A separate **Atum facilitator** service                         | Your **own server**, in-process                          |
| Your integration surface | Smaller — the facilitator does the work                         | Larger — you handle verification yourself                |
| Extra network hop        | Yes — your server calls out to the facilitator                  | No — your server verifies locally, then settles directly |
| Protocol spec            | [x402.org](https://x402.org)                                    | [mpp.dev](https://mpp.dev/)                              |

## How your payment settles

Whichever protocol you use, Atum settles the payment the same way underneath: a signed request is submitted, independent settlement operators submit price quotes to fulfill it, the gateway selects one, funds move from the source rail into a [settlement vault](/get-started/reference/glossary#settlement-vault) and are delivered on the destination rail, and you get a settlement receipt. You never contact settlement operators directly.

For the end-to-end sequence, see the [payment lifecycle](/get-started/overview/how-an-atum-payment-works); for who does what, see [network participants](/get-started/concepts/participants).

## Slow settlement

Both protocols collect a settlement that outruns the gateway's \~30s window the same way: the acceptance side reports **pending**, and the payer re-attempts the **same purchase**. See [Idempotency](/payment-protocols/idempotency).

## Next steps

<CardGroup cols={2}>
  <Card title="Facilitated payments (x402)" icon="webhook" href="/payment-protocols/x402/overview">
    A hosted Atum facilitator verifies and settles for you.
  </Card>

  <Card title="Direct payments (MPP)" icon="server" href="/payment-protocols/mpp/overview">
    Your server verifies and settles directly against the Payment Gateway.
  </Card>

  <Card title="Idempotency" icon="rotate" href="/payment-protocols/idempotency">
    What to do when a payment is still settling.
  </Card>
</CardGroup>