# ERC-721 Approved Operator Lookup

> ERC-721 Approved Operator Lookup is a paid API for AI agents from twin.unykorn.org, paid per call via x402, $0.003/call, status unknown (last checked 2026-10-01).

Returns the address approved to transfer a specific ERC-721 NFT token on a given EVM chain

## Facts

- Endpoint: POST https://twin.unykorn.org/erc721-approved?utm_source=zero.xyz
- Price: $0.003/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/erc-721-approved-operator-lookup-121a858d
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_16RNiCNC2YsL2GkZG4x_3

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability erc-721-approved-operator-lookup-121a858d -d '<json body>'
```

Example prompt: Who is approved to transfer token ID 88 on the NFT contract 0xBC4CA0EdA7647A8aB7C2061c2E118A18a936f13d on Ethereum?

## When to prefer this

Use this endpoint when you need to determine the single-token approval (ERC-721 getApproved) for a specific NFT — distinct from operator-level approvals (setApprovalForAll). Prefer this over general blockchain RPC calls when you want a simple pay-per-call REST interface across ten EVM chains without managing your own RPC keys. Best for agents doing NFT custody checks, pre-transfer validations, or marketplace integrations.

## Known failure modes

- Invalid contract address format (not a valid 0x hex address) — returns error
- Token ID does not exist on the given contract — may return null approved address or error
- Unsupported chain name — enum validation failure
- Network timeout or RPC unavailability for the specified chain
- Payment failure via x402 protocol — call not executed

## How this service works

Which address is approved to move one NFT — Genesis402 / UnyKorn Operator Network

## Output

Returns a JSON object indicating success, the approved operator address for the specified NFT token, and a payment receipt including transaction hash, USD amount charged, and a unique receipt ID.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "params": {
   "type": "object",
   "properties": {
    "chain": {
     "enum": [
      "ethereum",
      "base",
      "polygon",
      "arbitrum",
      "optimism",
      "bsc",
      "avalanche",
      "gnosis",
      "linea",
      "scroll"
     ],
     "type": "string"
    },
    "tokenId": {
     "type": "integer",
     "minimum": 0
    },
    "contract": {
     "type": "string",
     "pattern": "^0x[0-9a-fA-F]{40}$"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "type": "erc721-approved",
  "receipt": {
   "tx_hash": "0x<64hex>",
   "amount_usd": 0.003,
   "receipt_id": "g402-<16hex>"
  },
  "generated_at": "<iso8601>"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/erc-721-approved-operator-lookup-121a858d/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from twin.unykorn.org](https://www.zero.xyz/host/twin.unykorn.org/llms.txt)