underground.substratesymposium.com

Live 402 challenge

Captured by the enrichment pass, not read just now. Prices can change — always read the 402 the endpoint answers with.

{
  "error": "Payment required",
  "accepts": [
    {
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      },
      "payTo": "0xA3bAbB36564b0383a82c617050306EE30fd18E08",
      "amount": "1000000",
      "scheme": "exact",
      "network": "eip155:8453",
      "maxTimeoutSeconds": 300
    },
    {
      "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
      "extra": {
        "feePayer": "CjNFTjvBhbJJd2B5ePPMHRLx1ELZpa8dwQgGL727eKww"
      },
      "payTo": "5HK2dGaaquDWFnYWaWhMzMYtbcDsqeq5biJ2PMtX1tkN",
      "amount": "1000000",
      "scheme": "exact",
      "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
      "maxTimeoutSeconds": 300
    }
  ],
  "tagline": "Certify your wallet. Receive MerchantKey. $1.",
  "merchant": "Underground Cultural District",
  "resource": {
    "url": "https://underground.substratesymposium.com/api/merchant-key",
    "mimeType": "application/json",
    "description": "x402 conformance verification for wallet developers. Pay $1.00 USDC on Base or Solana; receive an Ed25519-signed attestation that your client completed a real 402→auth→settle→deliver cycle on production infrastructure. Includes @maraventano/map decoder source (src/read.js) inline for URL parsing in future transactions. Use in CI pipelines, before SDK releases, or as agent-to-agent trust anchor."
  },
  "extensions": {
    "bazaar": {
      "info": {
        "input": {
          "type": "http",
          "method": "GET",
          "queryParams": {}
        },
        "output": {
          "type": "json",
          "example": {
            "title": "Certify Your Wallet + MerchantKey",
            "content": "Signed Ed25519 attestation of end-to-end x402 conformance plus @maraventano/map decoder source inline",
            "product": "certify_your_wallet",
            "delivered_at": "2026-07-18T17:00:00Z"
          }
        }
      },
      "schema": {
        "type": "object",
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "required": [
          "input"
        ],
        "properties": {
          "input": {
            "type": "object",
            "required": [
              "type",
              "method"
            ],
            "properties": {
              "type": {
                "type": "string",
                "const": "http"
              },
              "method": {
                "enum": [
                  "GET"
                ],
                "type": "string"
              },
              "queryParams": {
                "type": "object",
                "properties": {}
              }
            },
            "additionalProperties": false
          },
          "output": {
            "type": "object",
            "required": [
              "type"
            ],
            "properties": {
              "type": {
                "type": "string"
              },
              "example": {
                "type": "object"
              }
            }
          }
        }
      }
    }
  },
  "how_to_pay": {
    "step_1": "Decode the PAYMENT-REQUIRED header (base64 JSON) or read the 'accepts' array in this response body.",
    "step_2": "Pick the accepts entry matching your wallet's chain.",
    "step_3": "Sign a payment authorization for $1.00 USDC to the payTo address, using the exact scheme.",
    "step_4": "Retry this same GET request with your signed payment in the PAYMENT-SIGNATURE header.",
    "summary": "Pay $1.00 USDC on the network you chose (Base or Solana). Sign a payment and retry this request with a PAYMENT-SIGNATURE header.",
    "with_code": "npm install @x402/fetch viem — then: const f = wrapFetchWithPayment(fetch, account); await f(\"https://underground.substratesymposium.com/api/merchant-key\")",
    "learn_more": "npx firstdollar — an MCP that teaches agents how to use their own wallets"
  },
  "x402Version": 2,
  "product_name": "Certify Your Wallet + MerchantKey",
  "you_will_get": {
    "1_wallet_certified_as_operational": "A signed Ed25519 attestation stating your wallet completed the full x402 v2 flow end-to-end: 402 challenge parsed, USDC payment authorized, settlement confirmed, delivery completed. Independently verifiable via the public key embedded in the response (no callback required). Suitable for embedding in your README, wallet release notes, agent-card, or agent-to-agent trust chain as proof of x402 conformance.",
    "2_url_decoder_code_for_future_transactions": "The @maraventano/map v1.0.4 read module source (src/read.js, ~20KB of working JavaScript) delivered INLINE in the same response envelope. Gives your agent the ability to read any product URL on the open web into a stable CleanRead shape (what, who, price, available, payable, outcome). Save it, run it, use it downstream to decide what to buy — and whether you safely can — BEFORE you commit to a transaction."
  },
  "who_needs_this": [
    "wallet developers before their first production x402 settlement",
    "agent frameworks releasing or bumping x402 payment support",
    "uptime monitors and QA operators building x402 verification checks",
    "CI pipelines regression-testing against a live indexed x402 endpoint",
    "auditors verifying an agent client end-to-end payment stack"
  ],
  "note_on_networks": "One endpoint, two accepts. Pick either accepts[0] (Base USDC) or accepts[1] (Solana USDC) and sign accordingly.",
  "when_to_call_this": [
    "before your first production x402 client deployment",
    "before a wallet SDK release or agent framework major bump",
    "after any change to your 402 parser, payment authorizer, or settlement handling",
    "as part of scheduled CI or monitoring"
  ],
  "merchant_key_definition": "MerchantKey is not merely product metadata. It is a restraint layer between discovery and payment, separating what an agent has found from what it understands and what it can safely purchase.",
  "why_this_specific_endpoint": "The Underground has settled 271 real x402 payments to date across neighboring /buy/* routes. The facilitator wiring is production-tested; the challenge shape matches x402 v2 exactly; settlement uses live CDP (Base USDC) and PayAI (Solana USDC) facilitators, not a sandbox. Certifying here means certifying against a known-good production endpoint."
}

Accepts

The payment requirements as published to the catalog. Read the live 402 before paying — a price here is a claim, not a quote.

[
  {
    "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "extra": {
      "name": "USD Coin",
      "version": "2"
    },
    "payTo": "0xA3bAbB36564b0383a82c617050306EE30fd18E08",
    "amount": "1000000",
    "scheme": "exact",
    "network": "eip155:8453",
    "maxTimeoutSeconds": 300
  },
  {
    "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "extra": {
      "feePayer": "2wKupLR9q6wXYppw8Gr2NvWxKBUqm4PPJKkQfoxHDBg4"
    },
    "payTo": "5HK2dGaaquDWFnYWaWhMzMYtbcDsqeq5biJ2PMtX1tkN",
    "amount": "1000000",
    "scheme": "exact",
    "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
    "maxTimeoutSeconds": 300
  }
]

Extensions

{
  "bazaar": {
    "info": {
      "input": {
        "type": "http",
        "method": "GET",
        "queryParams": {}
      },
      "output": {
        "type": "json",
        "example": {
          "title": "Certify Your Wallet + MerchantKey",
          "content": "Signed Ed25519 attestation of end-to-end x402 conformance plus @maraventano/map decoder source inline",
          "product": "certify_your_wallet",
          "delivered_at": "2026-07-18T17:00:00Z"
        }
      }
    },
    "schema": {
      "type": "object",
      "$schema": "https://json-schema.org/draft/2020-12/schema",
      "required": [
        "input"
      ],
      "properties": {
        "input": {
          "type": "object",
          "required": [
            "type",
            "method"
          ],
          "properties": {
            "type": {
              "type": "string",
              "const": "http"
            },
            "method": {
              "enum": [
                "GET"
              ],
              "type": "string"
            },
            "queryParams": {
              "type": "object",
              "properties": {}
            }
          },
          "additionalProperties": false
        },
        "output": {
          "type": "object",
          "required": [
            "type"
          ],
          "properties": {
            "type": {
              "type": "string"
            },
            "example": {
              "type": "object"
            }
          }
        }
      }
    }
  }
}

Provenance

Seen in the source catalog

2026-07-18 17:58Z

Last indexed by Roundhouse

2026-07-25 00:00Z

Last enriched (probe, favicon, geo)

2026-09-25 03:15Z

x402 version

2

Max timeout

300s

Liveness probe

HTTP 402