Trading Authorization | API Reference for Exchange, Trading, and DEX Integration

When engaging in decentralized trading through smart contracts, one of the foundational steps is transaction authorization. This process ensures that users maintain control over their assets while granting specific permissions to decentralized exchange (DEX) routers to execute trades on their behalf. Built on standards like ERC-20, this mechanism is essential for secure and seamless token swaps across blockchain networks.

This guide dives into the Trading Authorization API, a critical component for developers integrating DEX functionality into wallets, trading platforms, or DeFi applications. Whether you're building a cross-chain aggregator or enabling token approvals within a dApp, understanding how to correctly structure and use this API is key to delivering a smooth user experience.

What Is Trading Authorization?

In the context of decentralized finance (DeFi), trading authorization refers to the process where a user grants an approved smart contract — such as a DEX router — permission to spend a certain amount of their ERC-20 tokens. Without this approval, no automated trade can occur, even if the user initiates a swap.

The欧易 DEX router operates under this standard security model. Before any token exchange takes place, users must first approve the router contract to access their funds up to a specified limit. This API provides the necessary transaction parameters required to initiate that approval securely.

👉 Discover how to integrate secure token approvals into your dApp with powerful tools and real-time data.

Core Keywords

To ensure optimal search visibility and relevance, here are the core keywords naturally integrated throughout this article:

Trading Authorization
DEX API
Exchange API
API Reference
Token Approval
Smart Contract Interaction
ERC-20 Standard
Decentralized Trading

These terms reflect common search intents from developers, blockchain architects, and DeFi enthusiasts seeking technical documentation and implementation guidance.

API Endpoint: Retrieve Authorization Transaction Data

To begin the authorization flow, your application must query the following endpoint to retrieve the correct transaction data:

GET https://web3.okx.com/api/v5/dex/aggregator/approve-transaction

This endpoint returns all necessary parameters to construct a valid approval transaction on-chain. It supports multiple blockchains and adapts to token-specific decimal precision, ensuring compatibility across diverse ecosystems.

Request Parameters

To successfully call the API, include the following required parameters:

Parameter	Type	Required	Description
`chainIndex`	String	Yes	Unique identifier for the blockchain (e.g., `1` for Ethereum). For a full list, see supported chains documentation.
`chainId`	String	Yes	Legacy chain identifier. This field is deprecated but still required during transition.
`tokenContractAddress`	String	Yes	Contract address of the ERC-20 token (e.g., `0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48` for USDC).
`approveAmount`	String	Yes	Amount of tokens to approve, including decimals. For example: – Approving `1.00 USDT` → input `1000000` (6 decimals) – Approving `1.00 DAI` → input `1000000000000000000` (18 decimals)

⚠️ Note: Always validate the token’s decimal precision before formatting the approveAmount. Incorrect values may lead to failed transactions or unintended spending limits.

Response Parameters

Upon a successful request, the API returns the following response structure:

Parameter	Type	Description
`data`	String	The call data (ABI-encoded function call) to be sent in the transaction.
`dexContractAddress`	String	The欧易 DEX approval contract address (e.g., `0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48`). This is the spender address.
`gasLimit`	String	Recommended gas limit (e.g., `50000`). For more accurate estimates, refer to the `/gas-limit` endpoint.
`gasPrice`	String	Current gas price in wei (e.g., `110000000`). Use this to estimate transaction cost.

This data can be directly used by wallet providers or front-end interfaces to prompt users for signature via Web3 libraries like ethers.js or web3.js.

Example Request

Here’s an example of how to construct a GET request using query parameters:

GET /api/v5/dex/aggregator/approve-transaction?
  chainIndex=1&
  chainId=1&
  tokenContractAddress=0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48&
  approveAmount=1000000
Host: web3.okx.com

This request asks for approval of 1 USDC on the Ethereum network.

Example Response

{
  "data": "0x095ea7b3000000000000000000000000...",
  "dexContractAddress": "0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D",
  "gasLimit": "55000",
  "gasPrice": "110000000"
}

You can now use these values to build and broadcast the transaction using a connected wallet provider.

👉 Streamline your development workflow with real-time API responses and reliable transaction data.

Frequently Asked Questions (FAQ)

Q: Why do I need to approve tokens before trading?

Token approval is a security feature defined by the ERC-20 standard. It prevents unauthorized spending of your assets. Without approval, a DEX router or smart contract cannot move your tokens, even if you initiate a trade.

Q: What happens if I approve an infinite amount?

Some interfaces allow “infinite” approvals (e.g., max uint256). While convenient (fewer future approvals), it increases risk if the spender contract is compromised. It's safer to approve only what you need.

Q: Can I revoke an approval?

Yes. You can revoke approvals via blockchain explorers like Etherscan or through wallet tools like MetaMask or Rabby. Revoking stops all future spending by that contract.

Q: Is this API compatible with all EVM chains?

Yes, as long as the chain is supported by欧易 DEX and uses the ERC-20 standard. Use the correct chainIndex and verify token addresses per network.

Q: How do I handle different token decimals?

Always fetch the token’s decimals() value from its contract before formatting approveAmount. Libraries like ethers.js make this easy with contract calls.

Q: What does “chainId is deprecated” mean?

The chainId parameter will be phased out in favor of chainIndex, which offers clearer mapping across multi-chain environments. Continue including it until full deprecation.

Best Practices for Secure Implementation

Validate Inputs: Ensure tokenContractAddress and approveAmount are correctly formatted.
Use Latest Gas Data: Rely on dynamic gas estimation endpoints for accurate fees.
Inform Users: Clearly display what they’re approving — including token name and amount.
Support Revocation: Offer users an easy way to revoke permissions post-trade.

Developers should also monitor for changes in contract addresses or API deprecations by subscribing to official欧易 developer updates.

👉 Access advanced trading APIs with low latency and high reliability — start building today.

By leveraging the Trading Authorization API, developers gain fine-grained control over user permissions and transaction integrity. Whether you're building a next-gen wallet, DeFi dashboard, or cross-chain bridge, mastering token approvals is a foundational step toward secure, user-centric design.

With clear documentation, predictable responses, and broad chain support, this API simplifies one of DeFi’s most critical interactions — making decentralized trading safer and more accessible for everyone.