<!-- Markdown copy of https://insumermodel.com/check-the-payer/ for agents. -->

> One POST /v1/attest on the paying wallet returns a signed yes or no, never a balance. You decide whether to serve, change the terms, or decline.
>
> Page: https://insumermodel.com/check-the-payer/ · API: https://api.insumermodel.com · OpenAPI: https://insumermodel.com/openapi.json · Index for agents: https://insumermodel.com/llms.txt

[Developers](https://insumermodel.com/developers/) / Check the payer

# Check the wallet that pays you, then decide

You sell to agents: an x402 endpoint, a paid MCP server, an A2A service, a marketplace listing, an API. Before you serve a request, you can check the paying wallet with one call and get back a signed yes or no. What happens next is up to you.

This page is for the seller. If you are building the agent that pays, read [AI Agent Wallet Auth API](https://insumermodel.com/ai-agent-verification-api/) instead.

## The check

One `POST /v1/attest` on the paying wallet, before you serve. Send the wallet and up to 10 conditions, each with its own `chainId`, on any of 37 chains. The answer is a signed yes or no for each condition, plus `pass` for the whole set. It never returns a balance.

If you sell over x402, take the wallet from the signed payment payload rather than from a field the caller typed. The [x402 seller example](https://github.com/insumerapi/insumer-examples/blob/main/x402-condition-gate.js) shows how.

## Questions a seller usually asks

| Condition | What it answers | Where |
|---|---|---|
| erc8004_agent | Is this wallet registered as ERC-8004 agent N? Registration is open to anyone, so a yes means registered and nothing more. | Base, chainId 8453, only |
| erc7710_delegation | Does this wallet hold a valid, unrevoked delegation from the principal it says it acts for, and what limits did that principal sign? | Base, chainId 8453, only |
| ratio_to_amount | Does the wallet hold X times this payment? You send the multiple and the amount with each request, so one rule fits every price. | EVM chains |
| account_code | Is the wallet a contract or a plain key? | EVM chains |

Also available: `token_balance`, `nft_ownership`, `eas_attestation`, `farcaster_id`. Request fields for each are in the [developer docs](https://insumermodel.com/developers/) and [openapi.yaml](https://insumermodel.com/openapi.yaml).

## You decide

InsumerAPI reads chain state and signs what it found. It does not decide anything about the payer. You read `pass` and each result's `met`, then choose:

- **Serve** the request as priced.
- **Change the terms**: a different price, a smaller scope, a shorter session.
- **Ask for more**: another condition, a delegation, a second wallet.
- **Decline.**

The rule is yours, and so is the decision.

## Keep the answer

Every answer is signed twice: ES256 and a post-quantum ML-DSA-65 signature. The public keys are published as JWKS at [`/.well-known/jwks.json`](https://insumermodel.com/.well-known/jwks.json) and `GET /v1/jwks`. Each result carries a `conditionHash` of the exact condition that was evaluated, so your record shows the question as well as the answer. Add `proof: "merkle"` to get a Merkle proof against the block (27 of the 31 EVM chains). Check any of it offline with insumer-verify, on [npm](https://www.npmjs.com/package/insumer-verify) and [PyPI](https://pypi.org/project/insumer-verify/). No call back to the API.

An attestation is good for 30 minutes (5 when it includes a delegation). As a record of what you checked before you served, it is good for as long as you keep it.

## Paying for the check

x402 moves the money. InsumerAPI checks the conditions.

**x402, no key.** Send the request with no key, take the 402 quote, pay it in USDC on Base, Polygon, Arbitrum, Arc, or Solana, and retry. A check costs $0.05 a call, or $0.10 with a Merkle proof, with no key and no signup. Here you are the payer. The payer is charged only for a successful answer, and the payer sees the answer only after the payment settled.

**A key.** Free (10 credits), Pro $29/mo (1,000 credits), or Enterprise $99/mo (5,000 credits). A check is 1 credit, or 2 with a Merkle proof. Send the key in the `X-API-Key` header. Details on [pricing](https://insumermodel.com/pricing/).

## One call

The example below asks three things about the wallet that is paying you $5: is it registered as agent 1234, does it hold 10 times the payment, and is it a plain key rather than a contract. Swap in your own values.

POST /v1/attest:

```bash
curl -X POST https://api.insumermodel.com/v1/attest \
  -H "X-API-Key: $INSUMER_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "wallet": "0xYOUR_PAYER_WALLET",
    "conditions": [
      {
        "type": "erc8004_agent",
        "chainId": 8453,
        "agentId": "1234",
        "label": "Registered agent 1234"
      },
      {
        "type": "ratio_to_amount",
        "chainId": 8453,
        "contractAddress": "0x833589fcd6edb6e08f4c7c32d4f71b54bda02913",
        "multiple": "10",
        "amount": "5",
        "label": "Holds 10x the payment"
      },
      {
        "type": "account_code",
        "chainId": 8453,
        "expect": "none",
        "label": "Plain key account"
      }
    ]
  }'
```

No key? Drop the `X-API-Key` line. The first reply is the 402 quote; pay it and retry with the `PAYMENT-SIGNATURE` header.

Response shape (abridged):

```json
{
  "ok": true,
  "data": {
    "attestation": {
      "id": "ATST-A7C3E1B2D4F56789",
      "pass": true,
      "results": [
        { "condition": 0, "type": "erc8004_agent", "chainId": 8453, "met": true, "label": "Registered agent 1234", "conditionHash": "0x..." }
      ],
      "attestedAt": "...",
      "expiresAt": "..."
    },
    "sig": "...",
    "kid": "insumer-attest-v2",
    "pqSig": "...",
    "pqKid": "insumer-attest-pq1"
  },
  "meta": { "creditsCharged": 1 }
}
```

`data.attestation.pass` is true only when every condition is met. Each entry in `results` carries `met`, `chainId`, `label` and `conditionHash`. `sig`, `kid`, `pqSig` and `pqKid` are the two signatures and their key IDs.

## Next

- [Developer docs](https://insumermodel.com/developers/) and [openapi.yaml](https://insumermodel.com/openapi.yaml) for every field.
- [Pricing](https://insumermodel.com/pricing/) for credits and x402 rates.
- [x402 seller example](https://github.com/insumerapi/insumer-examples/blob/main/x402-condition-gate.js): an x402 endpoint that checks the payer's wallet before it charges.
- [The agent's side](https://insumermodel.com/ai-agent-verification-api/): MCP server, SDKs, and how an agent pays.

Need merchant screens (a dashboard, a scanner, passes)? Those are [Skye Meta](https://skyemeta.com/)'s, which builds on InsumerAPI.