A runnable client + server pair demonstrating the x402 (HTTP-402) agentic-payment flow on the XRP Ledger.

Both are wired into CI: the integration test X402ExampleClientServerE2E boots the server on real Kestrel and drives the client against it over loopback HTTP, against the standalone rippled used by the rest of the integration suite.

Both apps read their settings from their own appsettings.json (the X402 section) — strict JSON, so it lists every knob. Each value can be overridden by an environment variable (e.g. MERCHANT_ADDRESS, PAYER_SEED) without editing the file.

The port comes from the launch profile (launchSettings.json, http://127.0.0.1:5402) unless ListenUrl is set. Runs from Visual Studio (F5) or dotnet run. The committed MerchantAddress is a throwaway standalone-funded sample — replace it with your own.

RLUSD is a non-standard 5-character code, so it appears as the 40-hex currency 524C555344000000000000000000000000000000. For an IOU the price is a decimal token value (not drops), the asset needs an issuer, and the client only pays an IOU when an explicit per-issuer cap is present (IOU payments fail closed otherwise). The values below use Ripple's mainnet RLUSD issuer rMxCKbEDwqr76QuheSUMdEGf4B9xJ8m5De.

Server — X402.MerchantServer/appsettings.json (charge 2.5 RLUSD):

{
  "X402": {
    "RippledWsUrl": "wss://xrplcluster.com",
    "ListenUrl": "",
    "MerchantAddress": "rMerchantYouControl00000000000000000",
    "Network": "xrpl:1",
    "Asset": "524C555344000000000000000000000000000000",
    "IouIssuer": "rMxCKbEDwqr76QuheSUMdEGf4B9xJ8m5De",
    "Amount": "2.5",
    "MaxTimeoutSeconds": 60,
    "InvoiceId": "example-invoice-rlusd-001",
    "ResourceBody": "premium content"
  }
}

Client — X402.PayingClient/appsettings.json (allow up to 5 RLUSD from that issuer):

{
  "X402": {
    "RippledWsUrl": "wss://xrplcluster.com",
    "ResourceUrl": "http://127.0.0.1:5402/paid",
    "PayerSeed": "",
    "Network": "xrpl:1",
    "MaxAmountDrops": 10000000,
    "IouValueCaps": {
      "rMxCKbEDwqr76QuheSUMdEGf4B9xJ8m5De": 5.0
    }
  }
}

Notes:

• The IouValueCaps key is the same issuer as the server's IouIssuer (the client receives it as extra.issuer in the challenge); the value is a ceiling in token units (5.0 ≥ the 2.5 price).
• MaxAmountDrops only caps XRP — it does not apply to IOUs, which is why the cap entry is required.
• On-ledger prerequisites (else settlement fails with tecPATH_DRY / tecNO_LINE): the payer has an RLUSD trustline to the issuer and a balance ≥ the price; the merchant also has an RLUSD trustline; the issuer has DefaultRipple enabled.
• Mainnet uses real funds. For local testing, point RippledWsUrl at a standalone node and use your own issuer instead — the live test X402T54LiveInteropTests.TestILiveT54SettlesRlusdOnTestnet shows the full self-issued setup (issuer → trustlines → RLUSD issuance → payment with SendMax).

You need a reachable rippled (a standalone node or testnet) and two funded wallets — one for the merchant (receives) and one for the payer (signs/funds). For a standalone node, see the integration setup in the repo root README.

1. Start the merchant (Visual Studio F5, or terminal A). Set MerchantAddress in appsettings.json, then:

dotnet run --project Examples/X402.MerchantServer

For an IOU/RLUSD price, set Asset (40-hex currency code), IouIssuer, and an Amount decimal value (e.g. 2.5) in appsettings.json; the payer needs a trustline to that issuer.

2. Pay from the client (terminal B). The seed is a secret, so pass it via the environment:

PAYER_SEED="sEdPayerSeed..." dotnet run --project Examples/X402.PayingClient

The client prints the resource body plus the settlement receipt (success, tx hash, payer). The server settles but never submits the client's funds itself — the client signs locally and the merchant's facilitator settles, per the t54 scheme. See the full x402 guide for the complete price → pay → receipt flow.