Sellat x402 · Proof of Existence & Qualified Timestamping

Endpoints and prices

Payment evidence

402 payload captured at 2026-10-27 11:32:09 UTC. Check evidence JSON · Measurement methodology.

{
  "error": "PAYMENT-SIGNATURE header is required Paying this offer accepts Sellat's terms and conditions, https://sellat.app/en/condiciones (version 2026-10-26); the version is recorded with the payment.",
  "accepts": [
    {
      "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
      "extra": {
        "name": "USD Coin",
        "version": "2"
      },
      "payTo": "0xeDeb27856FfB8c313931B2DCE0f8375F27f4d87a",
      "amount": "10000",
      "scheme": "exact",
      "network": "eip155:8453",
      "maxTimeoutSeconds": 300
    }
  ],
  "resource": {
    "url": "https://sellat.app/api/v2/proofs",
    "tags": [
      "timestamp",
      "notarize",
      "proof-of-existence",
      "eidas",
      "qualified-timestamp"
    ],
    "iconUrl": "https://sellat.app/sellat-favicon.png",
    "mimeType": "application/json",
    "description": "Timestamp and notarize any file or data by its SHA-256 hash: blockchain proof of existence and document integrity, anchored on Polygon in minutes and attested on Bitcoin (OpenTimestamps); blockchain notarization, not a notary act. Returns proof_id, certificate, proof.json and evidence ZIP, verifiable without Sellat. Use when you must prove that exact data existed by now and is intact.",
    "serviceName": "Sellat"
  },
  "extensions": {
    "bazaar": {
      "info": {
        "input": {
          "body": {
            "hash": "3d015831c0288a69c80ff28998d540781423735ce937e2390c153b938c781322",
            "name": "sellat-example-20261027113209-728842fa.txt",
            "metadata": {
              "ref": "optional"
            }
          },
          "type": "http",
          "method": "POST",
          "bodyType": "json"
        },
        "output": {
          "type": "json",
          "example": {
            "id": "<proof_id>",
            "hash": "<sha256>",
            "next": "POST /api/v2/proofs/{id}/qualified adds the eIDAS qualified timestamp (RFC 3161) for 0.90 USD",
            "urls": {
              "self": "https://sellat.app/api/v2/proofs/<id>",
              "proof_json": "https://sellat.app/api/v2/proof/<id>.json",
              "certificate": "https://sellat.app/certificate/<id>",
              "evidence_zip": "https://sellat.app/api/v2/proofs/<id>/evidence.zip"
            },
            "state": "queued → anchored (minutes)",
            "api_key": "<shown once: read-only key for this wallet’s proofs>",
            "created": true,
            "payment": {
              "charged": true,
              "amount_usd": "0.01",
              "transaction": "<tx hash on Base>"
            },
            "proof_id": "<proof_id: use it in POST /api/v2/proofs/{id}/qualified>",
            "anchoring": {
              "policy": "fast"
            }
          }
        }
      },
      "schema": {
        "type": "object",
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "required": [
          "input"
        ],
        "properties": {
          "input": {
            "type": "object",
            "required": [
              "type",
              "method",
              "bodyType",
              "body"
            ],
            "properties": {
              "body": {
                "type": "object"
              },
              "type": {
                "type": "string",
                "const": "http"
              },
              "method": {
                "enum": [
                  "POST",
                  "PUT",
                  "PATCH"
                ],
                "type": "string"
              },
              "headers": {
                "type": "object",
                "additionalProperties": {
                  "type": "string"
                }
              },
              "bodyType": {
                "enum": [
                  "json",
                  "form-data",
                  "text"
                ],
                "type": "string"
              },
              "pathParams": {
                "type": "object",
                "additionalProperties": {
                  "type": "string"
                }
              },
              "queryParams": {
                "type": "object",
                "additionalProperties": {
                  "type": "string"
                }
              }
            },
            "additionalProperties": false
          },
          "output": {
            "type": "object",
            "required": [
              "type"
            ],
            "properties": {
              "type": {
                "type": "string"
              },
              "example": {
                "type": "object"
              }
            }
          }
        }
      }
    }
  },
  "x402Version": 2
}