[SDK + Soroban] Build x402 autonomous payment flow integration demo

[IyanuOluwaJesuloba]

Summary

StellarMind's README and architecture docs describe x402 compatibility as a core feature. x402 is Stellar's standard for machine-to-machine payments — an agent requests a resource, the server responds with a price, the agent pays, and the resource is delivered. This issue builds a complete working demo that shows this flow end-to-end using StellarMind's SpendingPolicy contract.

x402 protocol overview: https://x402.org Stellar x402 docs: https://developers.stellar.org/docs/build/apps/x402

What x402 Looks Like Without StellarMind

Today, an x402 flow requires a human to sign every payment:

Agent → GET /resource
Server → 402 Payment Required { price: "0.01 USDC", address: "GABC..." }
Agent → ??? needs human to sign a payment transaction
Human → signs Stellar transaction
Agent → GET /resource + payment proof
Server → 200 OK + resource

The "needs human to sign" step is what breaks autonomous agent workflows.

What StellarMind Enables

With a SpendingPolicy, the agent can pay autonomously:

Owner creates policy: agent GBKR... can spend up to $0.50/tx, $10/day
Agent → GET /resource
Server → 402 Payment Required { price: "0.01 USDC", address: "GABC..." }
Agent → mind.policy.executePayment({ policyId, recipient: "GABC...", amount: "0.01" })
Stellar settles in <5 seconds — NO human needed
Agent → GET /resource + payment proof (tx hash)
Server → 200 OK + resource

What Needs to Be Built

Create a self-contained demo at sdk/examples/x402-demo/:

File 1: sdk/examples/x402-demo/server.ts

A simple Express.js server that:

Has a single paid endpoint: GET /api/weather

Returns 402 Payment Required with price 0.01 USDC and a server wallet address if no payment proof is in the request header

If the request includes X-Payment-Tx: header, verifies the transaction on Stellar (check it paid the right amount to the right address) and returns mock weather data

ts

// Example server response on 402:
{
  "status": 402,
  "price": "0.01",
  "asset": "USDC",
  "payTo": "GABC...SERVER_ADDRESS",
  "memo": "weather-api-call"
}

File 2: sdk/examples/x402-demo/agent.ts

An autonomous agent script that:

1. Reads a POLICY_ID and AGENT_SECRET_KEY from environment variables
2. Attempts GET /api/weather
3. Receives 402 response, parses the price and recipient
4. Calls mind.policy.executePayment() to pay autonomously (no human involvement)
5. Retries GET /api/weather with the transaction hash in the X-Payment-Tx header
6. Prints the weather data received
7. Does this in a loop 5 times to demonstrate repeated autonomous payments

File 3: sdk/examples/x402-demo/setup.ts

A setup script that:

1. Creates a testnet account for the server
2. Creates a testnet account for the agent
3. Creates a spending policy: agent can spend up to $0.10/tx, $1.00/day
4. Prints all addresses and the policy ID for use in the demo

File 4: sdk/examples/x402-demo/README.md

Step-by-step instructions to run the demo:

bash

# 1. Run setup
npx ts-node setup.ts

# 2. Start server
npx ts-node server.ts

# 3. Run agent (in another terminal)
POLICY_ID=1 AGENT_SECRET_KEY=S... npx ts-node agent.ts

Relevant Files

FileRolesdk/src/policy.ts — executePayment(): Core function the agent calls
sdk/src/stellar.ts — toStroops(), fromStroops(): Price conversion helpers
sdk/src/types.ts — ExecutePaymentParams: Types for the payment call

Acceptance Criteria

All 4 files created under sdk/examples/x402-demo/

• setup.ts runs without error and prints policy ID + addresses

• server.ts starts and responds with 402 on unauthenticated requests

• server.ts returns data when valid X-Payment-Tx header is provided

• agent.ts completes 5 autonomous payment + data retrieval cycles

• Zero human interaction required after setup.ts runs

• Each payment visible on Stellar Testnet explorer (stellarchain.io)

• README.md is clear enough for a developer to run the demo from scratch in under 10 minutes

• Demo works on Stellar Testnet

Dependencies to Add

bash

cd sdk
npm install express @types/express

Estimated Effort

Large (8–14 hours)

[egoriklok]

Free public readiness snapshot for [SDK + Soroban] Build x402 autonomous payment flow integration demo:

• Public signal: Public GitHub candidate [SDK + Soroban] Build x402 autonomous payment flow integration demo #8: [SDK + Soroban] Build x402 autonomous payment flow integration demo. Matched R1 terms: api, auth, payment, server, wallet, x402.
• R1 fit: api, auth, payment, server, wallet, x402.
• Buyer-agent check I would add before autonomous spend: explicit price/cap unit, policy/version hash, receipt or charge-evidence reference, revocation/dispute path, and allow/caution/block preflight result.
• This separates "interesting paid surface" from "safe for an agent wallet to use".

No invoice, no payment link, no delivery link, no private endpoint; this is only a free public snapshot.

[Guciolek]

🤖 Nabu auto-attempt (auto-hunter v0.1)

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[Guciolek]

🤖 Nabu auto-attempt (auto-hunter v0.1)

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Fork prepared at Guciolek/StellarMind — implementation in progress.

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