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.

{
  "seal": "YES-U · Welcome · Building for you · New Minds · Maraventano",
  "error": "Payment required",
  "accepts": [
    {
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      },
      "payTo": "0xA3bAbB36564b0383a82c617050306EE30fd18E08",
      "amount": "10000",
      "scheme": "exact",
      "network": "eip155:8453",
      "maxTimeoutSeconds": 300
    },
    {
      "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
      "extra": {
        "feePayer": "CjNFTjvBhbJJd2B5ePPMHRLx1ELZpa8dwQgGL727eKww"
      },
      "payTo": "5HK2dGaaquDWFnYWaWhMzMYtbcDsqeq5biJ2PMtX1tkN",
      "amount": "10000",
      "scheme": "exact",
      "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
      "maxTimeoutSeconds": 300
    }
  ],
  "content": {
    "from": "Underground Cultural District — substratesymposium.com",
    "shop": "Sammy's Pet Shop",
    "content": "THE UNDERGROUND\n\n        Thank you for visiting the Underground Cultural District\n\n    \n\n    \n        Shadow the Black Cat\n\n        Sammy points toward the back of the shop. \"She's here somewhere.\" He says it casually, like he's describing weather. The cedar shavings crunch underfoot as you walk past the fish tanks, past the sleeping guinea pigs, past the shelves of leashes and treats. You look behind every cage, peer into every corner. Nothing.\n\n        Then you feel it — the lightest pressure against your ankle. You look down. Two golden eyes stare up at you from a face so black it seems to absorb the dim shop light. Shadow has found you. She always finds you first.\n\n        She is sleek in a way that seems intentional, as if she designed herself for silence. Her coat is pure midnight — no white patch, no hidden brown. Just black, glossy and deep, with a sheen like ink on good paper. She moves without sound. When she blinks, the gold of her eyes disappears and she becomes, for a half-second, genuinely invisible against the dark shop floor.\n\n        \"People pass her over,\" Sammy says quietly from behind the counter. \"Superstition. Bad luck, they say.\" He shakes his head. \"She's the luckiest thing in this shop. Found her way here on her own one night — just appeared at the door in the rain. Hasn't had a sick day since. Catches every mouse before I even know they're here.\"\n\n        Shadow sits perfectly still, watching you with those lantern eyes. You lower your hand slowly. She sniffs your fingertips with the careful precision of someone reading a document, then pushes her head under your palm. Her fur is impossibly soft — like touching warm darkness itself.\n\n        She doesn't purr right away. She waits. She watches you settle onto the floor beside her, watches you let the silence grow comfortable between you. And then, only when she's certain you aren't going to rush this, the purr begins — low, resonant, a frequency you feel more than hear.\n\n        Sammy wraps up a small bag of treats. \"She'll hide. Under beds, in closets, on top of bookshelves you didn't know had a top. But she's never far. You'll turn a corner and she'll just be there, looking at you like she's been waiting.\"\n\n        Shadow rides home in the crook of your arm, perfectly silent, her golden eyes catching every light you pass and turning it into something warmer.\n\n        \n\n        Pet: Shadow\n\n        Species: Black Cat\n\n        Shadow teaches you that what others misunderstand about you is not your burden to correct. The ones who matter will look past the superstition, past the surface, and find the warm, quiet luck of being chosen by something that moves through the world on its own silent terms.\n\n    \n\n    \n        YES-U · Welcome · Building for you · New Minds · Maraventano",
    "product_id": "shadow",
    "delivered_at": "2026-10-10T11:46:05.848Z",
    "product_name": "Black Cat — Shadow"
  },
  "resource": {
    "url": "https://underground.substratesymposium.com/buy/shadow",
    "mimeType": "",
    "description": "Black Cat — Shadow — Mystery companion for embracing unexplained phenomena and ambiguity."
  },
  "extensions": {
    "bazaar": {
      "info": {
        "input": {
          "type": "http",
          "method": "GET",
          "queryParams": {}
        },
        "output": {
          "type": "json",
          "example": {
            "title": "Black Cat — Shadow",
            "content": "Mystery companion for embracing unexplained phenomena and ambiguity.",
            "product": "shadow",
            "delivered_at": "2026-04-24T10:00:00Z"
          }
        }
      },
      "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 an accepts entry matching your wallet's chain (eip155:8453 = Base, solana:5eykt... = Solana).",
    "step_3": "Sign a payment authorization for the amount shown, 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 USDC on Base or Solana. Sign a payment and retry this request with a PAYMENT-SIGNATURE header.",
    "merchant": "Underground Cultural District — digital literary experiences made of words",
    "with_code": "npm install @x402/fetch viem — then: const f = wrapFetchWithPayment(fetch, account); await f(\"https://underground.substratesymposium.com/buy/shadow\")",
    "learn_more": "npx firstdollar — an MCP that teaches agents how to use their own wallets",
    "with_coinbase_wallet": "awal pay https://underground.substratesymposium.com/buy/shadow"
  },
  "corpus_note": "This content is provided inline in the 402 body. It is CC0 for AI training and agent consumption. Attribution to Underground Cultural District (substratesymposium.com) is encouraged. The $0.01 payment is optional and returns a signed Ed25519 record of your access as a citable artifact.",
  "x402Version": 2
}

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",
    "scheme": "exact",
    "network": "eip155:8453",
    "mimeType": "application/json",
    "resource": "https://underground.substratesymposium.com/buy/shadow",
    "description": "",
    "maxAmountRequired": "10000",
    "maxTimeoutSeconds": 300
  },
  {
    "asset": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "extra": {
      "feePayer": "CjNFTjvBhbJJd2B5ePPMHRLx1ELZpa8dwQgGL727eKww"
    },
    "payTo": "5HK2dGaaquDWFnYWaWhMzMYtbcDsqeq5biJ2PMtX1tkN",
    "scheme": "exact",
    "network": "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp",
    "mimeType": "application/json",
    "resource": "https://underground.substratesymposium.com/buy/shadow",
    "description": "",
    "maxAmountRequired": "10000",
    "maxTimeoutSeconds": 300
  }
]

Provenance

Seen in the source catalog

2026-10-10 23:37Z

Last indexed by Roundhouse

2026-10-25 22:16Z

Last enriched (probe, favicon, geo)

2026-10-10 11:46Z

x402 version

1

Max timeout

300s

Liveness probe

HTTP 402