Payments Facilitator

The Nevermined Payments Facilitator is an enforcement and settlement engine for HTTP-native agent payments. It lets any API, agent, MCP tool, or protected resource get paid without running on-chain infrastructure — and it speaks two sibling payment protocols that settle against the same Nevermined Payment Plans:

• x402 — payment terms travel in a payment-required header and the payment is presented in payment-signature. Covers standard “pay-per-request” x402 and Nevermined’s programmable extension (nvm:erc4337 and nvm:card-delegation schemes, with smart accounts, session keys, and contract settlement).
• MPP (Merchant Payment Protocol) — the same plan, credits, and delegation, negotiated with an RFC 7235 WWW-Authenticate: Payment … challenge and an Authorization: Payment … credential instead.

A request that costs 2 credits burns 2 whether it was paid over x402 or MPP: one meter, one delegation budget, two wire protocols. The Facilitator sits in the payment flow — when a server receives a payment token, it delegates verification and settlement to the Facilitator rather than handling it directly. See how the x402 flow works end to end.

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Why use a Facilitator?

A facilitator is the third party that:

• verifies payment proofs
• simulates/enforces what is allowed (amount, plan, merchant/agent binding)
• executes settlement on-chain
• returns a canonical receipt (e.g., transaction hash)

This is particularly important for programmable x402, where settlement may be more than a single ERC-20 transfer (credits, subscriptions, policy-based settlement).

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Facilitator API

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Environments

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Core Endpoints

Each protocol has its own verify/settle route pair. The plan, the credits, and the delegation underneath are identical — only the wire shape differs. x402 — verify then settle around your workload: MPP — a seller mints a challenge, then verifies and settles the credential the buyer returns: Buyers mint their access token at POST /api/v1/x402/permissions (x402) or POST /api/v1/mpp/permissions (MPP). A token minted for one protocol is refused on the other’s routes — see protocol isolation. Full MPP seller reference: Accepting MPP payments.

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How it works

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Nevermined’s programmable x402 extension

Standard x402 is often implemented as an “exact transfer” authorization (e.g., EIP-3009). Nevermined extends x402 to support:

• Smart Accounts (ERC-4337) and delegated session keys
• Smart-contract settlement (credits, subscriptions, PAYG, dynamic charging)
• Policy enforcement (merchant allowlists, spend caps, validity windows)

This keeps the HTTP handshake the same, but upgrades settlement from “transfer” to programmable execution.

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Facilitator responsibilities

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Verification

• x402 envelope structure/version
• signature authenticity
• session key validity + scoped permissions
• plan state + subscriber balance
• simulation of allowed on-chain actions (UserOps)

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Settlement

After the server completes its work, the facilitator can execute the settlement action permitted by the payment payload, such as:

• order (purchase/top-up)
• redeem / burn (consume credits)
• “exact” transfers (when using standard x402)

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Getting started