Trading Authorization | API Reference for Limit Orders and DEX Integration

In the rapidly evolving world of decentralized finance (DeFi), seamless and secure transaction execution is essential. One of the foundational steps in enabling DeFi interactions—especially when trading tokens on a decentralized exchange (DEX)—is trading authorization. This process allows users to grant permission to a DEX router contract to manage specific assets in their wallet, in accordance with the widely adopted ERC-20 Token standard.

This article provides a comprehensive overview of the trading authorization API, detailing how developers can retrieve the necessary transaction parameters to initiate token approvals securely and efficiently within Web3 applications.

Understanding Trading Authorization in DeFi

Before any token swap or liquidity provision can occur on a DEX, users must first authorize the DEX’s smart contract—often referred to as the router—to spend a specified amount of their ERC-20 tokens. Without this approval, the contract cannot interact with the user’s tokens, even if they are stored in a connected wallet.

The trading authorization API serves as a backend interface that returns critical data required to construct and broadcast an approval transaction. It eliminates guesswork by providing accurate call data, gas estimates, and contract addresses, ensuring smooth integration into dApps, wallets, or trading platforms.

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API Endpoint: Retrieve Approval Transaction Data

The trading authorization endpoint delivers all necessary parameters for constructing a valid ERC-20 approve() transaction. This is a GET request that returns structured data usable across Ethereum-compatible blockchains.

Request URL

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

This endpoint is designed for low-latency performance and high reliability, making it ideal for real-time dApp experiences.

Required Request Parameters

To generate accurate approval data, the following parameters must be included in the request:

Parameter	Type	Required	Description
`chainId`	String	Yes	The blockchain network ID (e.g., `1` for Ethereum Mainnet). See full list in supported networks documentation.
`tokenContractAddress`	String	Yes	The smart contract address of the ERC-20 token being approved (e.g., USDT: `0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48`).
`approveAmount`	String	Yes	The amount of tokens to approve, including decimals. For example: – 1.00 USDT (6 decimals) → `1000000` – 1.00 DAI (18 decimals) → `1000000000000000000`

These inputs ensure precision in token handling, preventing underflows, overflows, or incorrect approvals due to decimal misalignment.

Response Structure

Upon successful request, the API returns a JSON object containing key transaction details:

Field	Type	Description
`data`	String	The encoded function call data for the `approve()` method. Used in raw transaction construction.
`dexContractAddress`	String	The address of the DEX router contract that will be granted spending rights (e.g., `0x7a2fB7E6B5C8C5E8b5dDf4Cf8D4AcF3B5A627fEa`).
`gasLimit`	String	Recommended gas limit for the transaction (e.g., `50000`). Ensures sufficient execution capacity.
`gasPrice`	String	Current suggested gas price in wei (e.g., `110000000`). Helps optimize cost and speed.

This response enables developers to build fully signed transactions off-chain or through wallet providers like MetaMask, WalletConnect, or embedded WaaS solutions.

Example Usage Scenario

Imagine a user wants to trade USDC for WETH on a DEX integrated with OKX’s Web3 APIs. Before swapping:

The dApp calls the /approve-transaction endpoint with:
- chainId: "1"
- tokenContractAddress: "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48" (USDC)
- approveAmount: "2500000" (equivalent to 2.5 USDC)

The API returns:

{
  "data": "0x095ea7b3000...",
  "dexContractAddress": "0x7a2fB7E6B5C8C5E8b5dDf4Cf8D4AcF3B5A627fEa",
  "gasLimit": "50000",
  "gasPrice": "110000000"
}

The frontend uses this data to prompt the user’s wallet to sign the approval.

Only after confirmation can the actual swap proceed.

Frequently Asked Questions (FAQ)

What happens if I don't authorize a token before trading?

Without prior authorization, the DEX router cannot access your tokens. Any attempt to execute a trade will fail at the smart contract level, resulting in a reverted transaction and wasted gas fees.

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Can I revoke an existing approval?

Yes. Users can revoke allowances via blockchain explorers like Etherscan or through dedicated tools in wallets. Some advanced dApps also offer built-in revocation features to enhance security and reduce risks from compromised contracts.

Is there a risk in approving large amounts?

Approving excessively large amounts increases potential exposure if the approved contract is exploited. It's best practice to approve only what's needed—or use infinite approval cautiously and only with trusted protocols.

Why does approveAmount require decimal adjustment?

ERC-20 tokens use fixed-point arithmetic where amounts are represented in their smallest units (e.g., wei for ETH). Sending raw values without accounting for decimals leads to incorrect approvals—such as approving 1 million times less or more than intended.

How often do I need to re-authorize?

Once approved, the allowance remains active until spent or manually revoked. However, if you change wallets or clear dApp permissions, re-authorization is required.

Does this API support non-ERC-20 tokens?

Currently, this endpoint supports only ERC-20 compliant tokens on EVM-compatible chains. Support for other standards (e.g., BEP-20, ERC-721) may be available through separate endpoints.

Best Practices for Developers

Always validate chainId and tokenContractAddress against known lists to avoid spoofing.
Display estimated gas costs to users before initiating approval.
Offer options for “Approve Exact Amount” vs “Unlimited Approval” with clear warnings.
Cache gas prices intelligently but refresh frequently during volatile network conditions.
Integrate user-friendly error messages for common issues like insufficient balance or rejected transactions.

By following these guidelines, developers can create safer, more transparent DeFi experiences.

Final Thoughts

Trading authorization is not just a technical prerequisite—it's a cornerstone of secure and functional DeFi interactions. With reliable APIs like the one described here, developers can automate complex processes while maintaining full control over transaction integrity.

Whether you're building a multi-chain DEX aggregator, a limit-order protocol, or a Web3 wallet service, integrating accurate approval workflows enhances both performance and trust.

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