How to Enable Nevermined x402 USDC Payments for AI Agents (2026)

AI agents that charge other agents still trip over the same ops gap: you can return HTTP 402, but you still need a plan, a spend-capped buyer delegation, and a facilitator that verifies before work and settles after.

The named object is Nevermined Payments / Nevermined x402: register an agent plus a USDC ERC-20 plan (sandbox on Base Sepolia, then live), wire Express paymentMiddleware, have buyers createDelegation with provider: 'erc4337' and currency: 'usdc', mint an access token via getX402AccessToken, then verify/settle through Nevermined's facilitator. That is not Coinbase AgentKit as a third-party x402 client, not Circle's public x402 facilitator alone, not Cloudflare Agents MCP paywalls, not Privy agent wallet custody, and not Alchemy gateway auth for RPC credits.

Facts below come from Nevermined's 5-minute setup, Nevermined x402, and Express.js integration docs as of September 30, 2026. Code shapes, header names, Base Sepolia USDC address, scheme names, and the BCK.X402.0030 missing-delegationConfig error are taken from those pages. No invented fee schedules or unofficial facilitator URLs.

Key Takeaways

• Register agent + USDC plan with registerAgentAndPlan; match sandbox: / live: key to environment.
• Protect Express routes with paymentMiddleware(planId, credits); middleware verifies then settles.
• Buyers createDelegation(erc4337, usdc) first, then getX402AccessToken with that delegationId.
• Omit delegationConfig and you hit BCK.X402.0030; reuse one capped delegation across token mints.
• nvm:erc4337 settles via ERC-4337 UserOps and credits; card-delegation is the fiat sibling scheme.

Who this is for

Use this path if you expose an agent API, MCP tool, or protected HTTP resource, you want buyers to pay in USDC (or credits backed by a USDC plan) under spend caps, and you can run TypeScript Express or Python FastAPI with the Nevermined Payments SDK.

Skip it if you are only paying third-party x402 merchants (see How to Pay for an x402 API with Coinbase AgentKit), standing up Circle's facilitator without Nevermined plans (see How to Enable Circle x402 Facilitator for USDC), charging MCP tools on Cloudflare (see How to Charge for MCP Tools with Cloudflare Agents x402), provisioning TEE wallets (see How to Provision Privy Agent Wallets for USDC), or authenticating Alchemy RPC with x402 (see How to Authenticate Alchemy APIs with x402 USDC). For picking among facilitators, see How to Choose an x402 Facilitator for USDC. For generic accept-side patterns, see How to Accept x402 USDC Payments from AI Agents.

What Nevermined x402 means for USDC agent payments

Standard x402 focuses on EIP-3009-style pay-per-request ERC-20 transfers. Nevermined keeps the HTTP 402 handshake (payment-required / payment-signature / payment-response) and extends settlement with ERC-4337 smart accounts, session keys, and plan credits. The crypto scheme is nvm:erc4337 on networks such as eip155:84532 (Base Sepolia in the docs' examples). The fiat sibling is nvm:card-delegation (Stripe / Braintree / Visa).

Operators care about three objects: the agent (your monetizable service), the plan (price + credits or time window), and the buyer's delegation (spendingLimitCents, durationSecs, provider, currency). Settlement burns credits after work succeeds. With a live delegation, the facilitator can also top up credits automatically up to the cap, so buyers are not stuck in a manual orderPlan loop for every request.

MPP is the sibling wire format. Same plans, credits, and delegation; different handshake (WWW-Authenticate: Payment instead of an x402 accepts body). This guide stays on x402 USDC / nvm:erc4337.

Prerequisites and environment matching

Create an API key in nevermined.app under Settings → Global NVM API Keys. Nevermined documents two prefixes and backends:

Install the SDK: npm install @nevermined-io/payments (TypeScript) or pip install payments-py (Python). Keep a builder wallet address for USDC payouts on the plan. For sandbox USDC on Base Sepolia, Nevermined's 5-minute setup uses contract 0x036CbD53842c5426634e7929541eC2318f3dCF7e. Mainnet Base USDC is commonly 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913; confirm the address Nevermined's live plan config expects before you fund production.

Step 1: Register the agent and a USDC plan

Call payments.agents.registerAgentAndPlan with service metadata, an endpoint map, plan metadata, an ERC-20 price config, and a fixed-credits config. The 5-minute setup example prices 10 USDC (10_000_000 base units at 6 decimals) for 100 requests at 1 credit each.

TypeScript shape (from Nevermined's docs): initialize Payments.getInstance({ nvmApiKey, environment: 'sandbox' }), then pass getERC20PriceConfig(10_000_000n, USDC_ADDRESS, BUILDER_ADDRESS) plus getFixedCreditsConfig(100n, 1n). Persist the returned agentId and planId. You can also create agents and plans in the Nevermined App without code; the IDs still land in the same middleware.

Stablecoin Insider's operator note: register in sandbox first, hit the 402 path with a buyer key, then promote the same structure to live with a live: key. Do not mix sandbox plan IDs into a live Express process.

Step 2: Wire Express paymentMiddleware

For Express, Nevermined ships paymentMiddleware from @nevermined-io/payments/express. One middleware registration protects routes; handlers stay payment-free.

Minimal pattern from the Express guide: app.use(paymentMiddleware(payments, { 'POST /ask': { planId: PLAN_ID, credits: 1 } })). The middleware returns 402 with a payment-required header when the client omits payment-signature, verifies the token with the facilitator before your handler runs, burns credits on settle, and attaches a payment-response receipt. Route config also supports dynamic credits (for example based on token count), path parameters, and an explicit agentId when one plan covers multiple agents.

Manual path (any framework): build paymentRequired with buildPaymentRequired(PLAN_ID, { endpoint, agentId, httpVerb }); if no payment-signature, return 402 with base64 payment-required; else facilitator.verifyPermissions, run work, then facilitator.settlePermissions. Nevermined is explicit: verify does not burn credits; settle does.

Step 3: Buyer createDelegation (erc4337 / usdc) + getX402AccessToken

Buyers do not paste raw private keys into the agent. They create a spend-capped delegation, then mint short-lived x402 access tokens against it.

Required create-first flow (docs as of 2026): payments.delegation.createDelegation({ provider: 'erc4337', spendingLimitCents, durationSecs, currency: 'usdc' }), then payments.x402.getX402AccessToken(planId, agentId, { scheme: 'nvm:erc4337', delegationConfig: { delegationId } }). Reuse the same delegationId for subsequent token mints until the cap or duration expires. Inline create-on-the-fly fields inside delegationConfig are deprecated and warn at runtime.

If delegationConfig is missing, Nevermined surfaces BCK.X402.0030 at runtime. Treat that code as a configuration bug, not a chain outage. For fiat plans, create the delegation with a card provider and currency: 'usd', and pass scheme: 'nvm:card-delegation'; buyer-side getX402AccessToken defaults to crypto and will not auto-detect fiat.

Send the token on the next request:

payment-signature: <accessToken>

Optional orderPlan still works for an initial credit balance, but with a valid USDC/card delegation the facilitator can top up at settle time up to spendingLimitCents. That is the difference between a demo curl and an autonomous buyer agent.

Step 4: Verify, execute, settle

Server-side verify checks envelope structure, EIP-712 signature / session keys, UserOp simulation, delegated permissions (burn/order/redeem), and plan balance. On failure, return 402. On success, run the paid workload, then settle with the credits actually consumed. Include billingModel in the settlement receipt you echo back: on pay-as-you-go plans credit fields can read "0", so buyers need billingModel to tell a real charge from a no-op credits settle.

Ops checklist Stablecoin Insider recommends before live:

• Curl without payment-signature; expect 402 + payment-required.
• Mint a capped sandbox delegation ($10 / 1 day is the docs' example scale; see Nevermined 5-minute setup) and retry with payment-signature.
• Confirm creditsRemaining (or billingModel receipt) moves after settle.
• Revoke the delegation and confirm further settles fail.
• Only then switch to a live: key and mainnet plan IDs.

Spend caps, credits, and sandbox vs live

Delegations are the control plane. spendingLimitCents and durationSecs bound what an autonomous buyer can burn without a human in the loop. Credits on the plan are the metering unit your agent burns per request; USDC on the plan is how those credits get funded. Do not confuse "direct USDC per request" EIP-3009 x402 with Nevermined's credits + smart-account settle. Both speak HTTP 402; the settlement model differs.

Sandbox is for integration tests on Base Sepolia USDC. Live is production. Promote plans deliberately. If you need to fund a buyer wallet before first purchase, see How to Fund an AI Agent Wallet with USDC. If you need Stripe-shaped machine payments without Nevermined plans, see How to Accept Stripe MPP Payments in USDC.

How Nevermined compares to other x402 stacks

For a broader facilitator shortlist, use How to Choose an x402 Facilitator for USDC. Nevermined wins when you need plan objects, credit metering, and capped buyer delegations in one SDK. It is heavier than a bare facilitator URL if you only need a single EIP-3009 transfer per request.

Stablecoin Insider's take

FAQ

How to Choose an x402 Facilitator for USDC (2026)

Compare x402 facilitator options for USDC agent and API payments.

Stablecoin Insider

This content is provided for informational and educational purposes only and does not constitute financial, investment, legal, or tax advice; no material herein should be interpreted as a recommendation, endorsement, or solicitation to buy or sell.