---
title: "Allow the NFT auction or marketplace to transfer an asset"
method: POST
path: "/v3/blockchain/auction/approve"
tags: ["Auction"]
---

# Allow the NFT auction or marketplace to transfer an asset

`POST /v3/blockchain/auction/approve`

## Request

- Base URL: `https://api.tatum.io`
- URL: `https://api.tatum.io/v3/blockchain/auction/approve`
- Auth: API key in header `x-api-key`

/v3/blockchain/auction/approve

**2 credits per API call**

Allow the NFT auction/marketplace smart contract to transfer the asset (NFT or Multi Token) that is listed for selling.  
The auction/marketplace smart contract will transfer the asset to the buyer after the asset is purchased.

This API is supported for the following blockchains:

*   BNB Smart Chain
*   Celo
*   Ethereum
*   Harmony
*   Klaytn
*   Polygon

**Signing a transaction**  
When allowing the NFT auction/marketplace smart contract to transfer the asset, you are charged a fee for the transaction, and you must sign the transaction with the private key of the blockchain address from which the fee will be deducted.

Providing the private key in the API is not a secure way of signing transactions, because the private key can be stolen or exposed. Your private keys should never leave your security perimeter. You should use the private keys only for testing a solution you are building on the **testnet** of a blockchain.

For signing transactions on the **mainnet**, we strongly recommend that you use the Tatum [Key Management System (KMS)](https://github.com/tatumio/tatum-kms) and provide the signature ID instead of the private key in the API. Alternatively, you can use the [Tatum JavaScript client](https://github.com/tatumio/tatum-js/tree/v2).

## Request body

- union
  - ApproveNftSpending
    - `chain` 'BSC' | 'ETH' | 'KLAY' | 'MATIC' | 'ONE', required: The blockchain to work with
    - `spender` string, required: The blockchain address of the auction/marketplace smart contract
    - `isErc721` boolean, required: Set to "true" if the asset is an NFT; set to "false" is the asset is a Multi Token
    - `tokenId` string, required: The ID of the asset (NFT or Multi Token)
    - `contractAddress` string, required: The blockchain address of the smart contract from which the asset (NFT or Multi Token) was minted
    - `fromPrivateKey` string, required: The private key of the blockchain address from which the fee will be deducted
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` CustomFee: The custom defined fee; if not present, will be calculated automatically
      - `gasPrice` string, required: The price for one gas unit (in Gwei)
      - `gasLimit` string, required: The maximum number of gas units that you are willing to spend on processing the transaction at the provided gas price
  - ApproveNftSpendingKMS
    - `chain` 'BSC' | 'ETH' | 'KLAY' | 'MATIC' | 'ONE', required: The blockchain to work with
    - `spender` string, required: The blockchain address of the auction/marketplace smart contract
    - `isErc721` boolean, required: Set to "true" if the asset is an NFT; set to "false" is the asset is a Multi Token
    - `tokenId` string, required: The ID of the asset (NFT or Multi Token)
    - `contractAddress` string, required: The blockchain address of the smart contract from which the asset (NFT or Multi Token) was minted
    - `signatureId` string, uuid, required: The KMS identifier of the private key of the blockchain address from which the fee will be deducted
    - `index` number: (Only if the signature ID is mnemonic-based) The index of the address from which the fee will be deducted that was generated from the mnemonic
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` CustomFee: The custom defined fee; if not present, will be calculated automatically
      - `gasPrice` string, required: The price for one gas unit (in Gwei)
      - `gasLimit` string, required: The maximum number of gas units that you are willing to spend on processing the transaction at the provided gas price
  - ApproveNftSpendingCelo
    - `chain` 'CELO', required: The blockchain to work with
    - `spender` string, required: The blockchain address of the auction/marketplace smart contract
    - `isErc721` boolean, required: Set to "true" if the asset is an NFT; set to "false" is the asset is a Multi Token
    - `tokenId` string, required: The ID of the asset (NFT or Multi Token)
    - `contractAddress` string, required: The blockchain address of the smart contract from which the asset (NFT or Multi Token) was minted
    - `fromPrivateKey` string, required: The private key of the blockchain address from which the fee will be deducted
    - `feeCurrency` 'CELO' | 'CUSD' | 'CEUR', required: The currency in which the transaction fee will be paid
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` CustomFee: The custom defined fee; if not present, will be calculated automatically
      - `gasPrice` string, required: The price for one gas unit (in Gwei)
      - `gasLimit` string, required: The maximum number of gas units that you are willing to spend on processing the transaction at the provided gas price
  - ApproveNftSpendingCeloKMS
    - `chain` 'CELO', required: The blockchain to work with
    - `spender` string, required: The blockchain address of the auction/marketplace smart contract
    - `isErc721` boolean, required: Set to "true" if the asset is an NFT; set to "false" is the asset is a Multi Token
    - `tokenId` string, required: The ID of the asset (NFT or Multi Token)
    - `contractAddress` string, required: The blockchain address of the smart contract from which the asset (NFT or Multi Token) was minted
    - `signatureId` string, uuid, required: The KMS identifier of the private key of the blockchain address from which the fee will be deducted
    - `index` number: (Only if the signature ID is mnemonic-based) The index of the address from which the fee will be deducted that was generated from the mnemonic
    - `feeCurrency` string, required: The currency in which the transaction fee will be paid - CELO - CUSD - CEUR
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` CustomFee: The custom defined fee; if not present, will be calculated automatically
      - `gasPrice` string, required: The price for one gas unit (in Gwei)
      - `gasLimit` string, required: The maximum number of gas units that you are willing to spend on processing the transaction at the provided gas price

## Response `200`

OK

- union
  - TransactionHash
    - `txId` string, required: The hash (ID) of the transaction
  - SignatureId
    - `signatureId` string, uuid, required: The internal Tatum ID of the prepared transaction for Key Management Sysytem (KMS) to sign<br/>This is different from the <code>signatureId</code> parameter that you provided in the request body. The <code>signatureId</code> parameter in the request body specifies the signature ID associated with the private key in KMS.

## Other responses

- `400`: Bad Request
- `401`: Unauthorized. Not valid or inactive subscription key present in the HTTP Header.
- `403`: Forbidden. The request is authenticated, but it is not possible to perform the operation due to logical error or invalid permissions.
- `500`: Internal server error. There was an error on the server during the processing of the request.

---

[API](https://skmtc.dev/tatum/apis/smart-contracts.md) - [All operations](https://skmtc.dev/tatum/apis/smart-contracts/llms.txt) - [OpenAPI document](https://skmtc.dev/tatum/apis/smart-contracts/revisions/c0146043bb37?raw)