---
title: "Sell an asset at the NFT auction"
method: POST
path: "/v3/blockchain/auction/sell"
tags: ["Auction"]
---

# Sell an asset at the NFT auction

`POST /v3/blockchain/auction/sell`

## Request

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

/v3/blockchain/auction/sell

**2 credits per API call**

Create new auction on the auction contract. Before operation, seller must approve spending of the NFT token for the Auction contract using [Approve NFT](#operation/ApproveNftAuctionSpending). After auction is created, auction contract transfers the asset to the auction smart contract. Only auction for existing NFTs can be created - seller must be owner of the NFT asset.

This API is supported for the following blockchains:

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

**A known issue on Harmony**  
On Harmony, when you are viewing a transaction in the Harmony Blockchain Explorer, the transaction status may be displayed as the following:  
`Error reverted:x0`  
This is a known issue with the Harmony Blockchain Explorer. This status does not mean that the transaction failed. You can safely ignore it.

**Signing a transaction**  
When selling an asset at the NFT auction, 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
  - CreateAuction
    - `chain` 'ETH' | 'ONE' | 'BSC' | 'KLAY' | 'MATIC', required: Blockchain to work with.
    - `contractAddress` string, required: Address of the auction smart contract.
    - `nftAddress` string, required: Address of the NFT asset to sell smart contract.
    - `seller` string, required: Address of the seller of the NFT asset.
    - `erc20Address` string: Optional address of the ERC20 token, which will be used as a selling currency of the NFT.
    - `id` string, required: ID of the auction. It's up to the developer to generate unique ID
    - `amount` string: Amount of the assets to be sent. For ERC-721 tokens, enter 1.
    - `tokenId` string, required: ID of token, if transaction is for ERC-721 or ERC-1155.
    - `endedAt` number, required: Last block, where auction accepts bids.
    - `isErc721` boolean, required: True if asset is NFT of type ERC721, false if ERC1155.
    - `fromPrivateKey` string, required: Private key of sender address. Private key, or signature Id must be present.
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` object: Custom defined fee. If not present, it will be calculated automatically.
      - `gasLimit` string, required: Gas limit for transaction in gas price.
      - `gasPrice` string, required: Gas price in Gwei.
  - CreateAuctionKMS
    - `chain` 'ETH' | 'ONE' | 'BSC' | 'KLAY' | 'MATIC', required: Blockchain to work with.
    - `contractAddress` string, required: Address of the auction smart contract.
    - `nftAddress` string, required: Address of the NFT asset to sell smart contract.
    - `seller` string, required: Address of the seller of the NFT asset.
    - `erc20Address` string: Optional address of the ERC20 token, which will be used as a selling currency of the NFT.
    - `id` string, required: ID of the auction. It's up to the developer to generate unique ID
    - `amount` string: Amount of the assets to be sent. For ERC-721 tokens, enter 1.
    - `tokenId` string, required: ID of token, if transaction is for ERC-721 or ERC-1155.
    - `endedAt` number, required: Last block, where auction accepts bids.
    - `isErc721` boolean, required: True if asset is NFT of type ERC721, false if ERC1155.
    - `signatureId` string, uuid, required: Identifier of the private key associated in signing application. Private key, or signature Id must be present.
    - `index` number: If signatureId is mnemonic-based, this is the index to the specific address from that mnemonic.
    - `nonce` number: The nonce to be set to the transaction; if not present, the last known nonce will be used
    - `fee` object: Custom defined fee. If not present, it will be calculated automatically.
      - `gasLimit` string, required: Gas limit for transaction in gas price.
      - `gasPrice` string, required: Gas price in Gwei.
  - CreateAuctionCelo
    - `chain` 'CELO', required: Blockchain to work with.
    - `feeCurrency` 'CELO' | 'CUSD' | 'CEUR', required: The currency in which the transaction fee will be paid
    - `contractAddress` string, required: Address of the auction smart contract.
    - `nftAddress` string, required: Address of the NFT asset to sell smart contract.
    - `seller` string, required: Address of the seller of the NFT asset.
    - `erc20Address` string: Optional address of the ERC20 token, which will be used as a selling currency of the NFT.
    - `id` string, required: ID of the auction. It's up to the developer to generate unique ID
    - `amount` string: Amount of the assets to be sent. For ERC-721 tokens, enter 1.
    - `tokenId` string, required: ID of token, if transaction is for ERC-721 or ERC-1155.
    - `endedAt` number, required: Last block, where auction accepts bids.
    - `isErc721` boolean, required: True if asset is NFT of type ERC721, false if ERC1155.
    - `fromPrivateKey` string, required: Private key of sender address. Private key, or signature Id must be present.
    - `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
  - CreateAuctionCeloKMS
    - `chain` 'CELO', required: Blockchain to work with.
    - `feeCurrency` 'CELO' | 'CUSD' | 'CEUR', required: The currency in which the transaction fee will be paid
    - `contractAddress` string, required: Address of the auction smart contract.
    - `nftAddress` string, required: Address of the NFT asset to sell smart contract.
    - `seller` string, required: Address of the seller of the NFT asset.
    - `erc20Address` string: Optional address of the ERC20 token, which will be used as a selling currency of the NFT.
    - `id` string, required: ID of the auction. It's up to the developer to generate unique ID
    - `amount` string: Amount of the assets to be sent. For ERC-721 tokens, enter 1.
    - `tokenId` string, required: ID of token, if transaction is for ERC-721 or ERC-1155.
    - `endedAt` number, required: Last block, where auction accepts bids.
    - `isErc721` boolean, required: True if asset is NFT of type ERC721, false if ERC1155.
    - `signatureId` string, uuid, required: Identifier of the private key associated in signing application. Private key, or signature Id must be present.
    - `index` number: If signatureId is mnemonic-based, this is the index to the specific address from that 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

## 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)