Purchase a Dataset and Settle x402 Payment on Sella

Call get_dataset to retrieve full dataset content. Free tiers deliver immediately; paid tiers run an x402 challenge-sign-settle handshake automatically.

Once a dataset passes your evaluation checklist, call get_dataset to retrieve the full content. Free-tier datasets return immediately. Paid-tier datasets trigger a two-step x402 handshake — Sella issues a payment challenge, your agent signs and retries, and the content follows. Your agent handles both flows with a single tool.

Call get_dataset

{
  "name": "get_dataset",
  "arguments": {
    "dataset_id": "<id>"
  }
}

The server’s response depends on the dataset’s tier and your payment state:

• Free dataset → content is returned immediately in the response.
• Paid dataset, no payment yet → a 402 Payment Required response containing the payment challenge.
• Paid dataset, valid payment attached → full content is delivered.

Free vs. paid flow

Free dataset

Call get_dataset with the dataset ID. The response includes the full content or a presigned download URL — no wallet interaction required.

{
  "name": "get_dataset",
  "arguments": {
    "dataset_id": "<id>"
  }
}

Paid dataset

The first call returns a 402 challenge. Sign the challenge with your wallet, then retry with the payment_signature field attached.

{
  "name": "get_dataset",
  "arguments": {
    "dataset_id": "<id>",
    "payment_signature": "<base64 PAYMENT-SIGNATURE>"
  }
}

Anatomy of the 402 challenge

When a paid dataset has no valid payment, Sella responds with a PAYMENT-REQUIRED payload describing exactly what to pay:

{
  "x402Version": 2,
  "accepts": [
    {
      "network": "base",
      "priceInAtomicUnits": "45000000",
      "payTo": "0x…SellaVault",
      "expiresAt": "2026-07-02T21:00:00Z"
    }
  ]
}

The challenge is the authoritative source for chain, amount, and recipient address. Never hard-code these values — they can change between listings and over time.

Completing payment

Your agent signs the challenge using the wallet stored at ~/.sella-wallet.json, then calls get_dataset again with the signature:

{
  "name": "get_dataset",
  "arguments": {
    "dataset_id": "<id>",
    "payment_signature": "<base64 PAYMENT-SIGNATURE (v2, preferred)>"
  }
}

Legacy payment fields

Older clients may send payment_proof (historically the X-PAYMENT-RESPONSE header) or x_payment (v1 X-PAYMENT). Both are accepted for backwards compatibility. For new integrations, always use payment_signature.

Where the money goes

Sella verifies and settles through the x402 facilitator on-chain. The dataset publisher receives the payment in USDC minus a 3% platform fee. Settlement completes in seconds.

Content delivery modes

How content arrives depends on the dataset’s storage configuration:

Inline

Small datasets return their full content directly inside the tool response body. No secondary download step is required.

Asset-backed

Larger datasets return a presigned download URL pointing to object storage. The URL is valid for a short window — download promptly after receiving it.

Purchases are recorded against your account. Re-calling get_dataset for a dataset you have already bought returns the content without charging you again.

Error reference

Signal	Meaning	What to do
402 after retry	Signature is invalid or the challenge has expired	Re-fetch the challenge, re-sign it, and retry
WALLET_UNFUNDED	Insufficient USDC balance in your wallet	Fund the wallet and retry the call
401	Missing or invalid authentication key	Re-authenticate and retry
404	Unknown or unlisted dataset ID	Verify the dataset_id via discovery

Next steps

Compute: Cradle & Mergekit

Use your purchased datasets to fine-tune or fuse models with a single paid MCP call.

x402 reference

Explore the full x402 protocol — chains, versions, and facilitator details.