EVM Chains (Linea & Ethereum)

Overview

This guide covers EVM-specific implementation details for delegating wallets on Linea and Ethereum networks. Both networks follow the same ERC20 approval pattern with slight differences in gas costs and confirmation times.

Use the /v1/delegation/evm/post-approval endpoint for both Linea and Ethereum delegations.

Supported EVM Networks

Linea
Ethereum

Network Name: Linea Chain ID: 59144 (0xe708) RPC URL: https://rpc.linea.build Block Explorer: https://lineascan.build Currencies: USDC, USDTAdvantages:

Significantly lower gas fees than Ethereum mainnet
Faster block times (~2-3 seconds)
Primary network recommended for most integrations
US routing available with x-us-env: true header

Typical Gas Cost:

0.01 -

0.10 per transaction

ERC20 Approval Pattern

EVM delegation uses the standard ERC20 approve() function to grant spending authority.

The approve() Function

function approve(address spender, uint256 amount) public returns (bool)

Parameters:

spender: Platform’s smart contract address that will spend tokens
amount: Maximum amount the spender can transfer (in token’s smallest unit)

Returns: true if approval succeeded

How It Works

User Calls approve()

User’s wallet calls the approve() function on the token contract (USDC or USDT)

Allowance Updated

Token contract updates the allowance mapping:

allowances[userAddress][platformSpender] = amount

Platform Can Spend

Platform’s smart contract can now call transferFrom() to spend up to the approved amount

Allowance Decreases

Each time platform spends, the allowance decreases by the spent amount

Implementation

Contract Addresses

Obtain contract addresses dynamically by calling the chain configuration endpoint before starting the delegation flow:

const response = await fetch('https://api.baanx.com/v1/delegation/chain/config', {
  headers: {
    'x-client-key': process.env.CLIENT_PUBLIC_KEY!,
    'Authorization': `Bearer ${userAccessToken}`
  }
});

const config = await response.json();

const TOKEN_ADDRESSES = {
  linea: {
    chainId: config.linea.chain_id,         // 59144
    usdc: config.linea.usdc_address,        // Linea USDC contract
    usdt: config.linea.usdt_address,        // Linea USDT contract
    spender: config.linea.spender_address   // Platform spender for Linea
  },
  ethereum: {
    chainId: config.ethereum.chain_id,      // 1
    usdc: config.ethereum.usdc_address,     // Ethereum USDC
    usdt: config.ethereum.usdt_address,     // Ethereum USDT
    spender: config.ethereum.spender_address // Platform spender for Ethereum
  }
};

Recommended: Always fetch addresses dynamically using GET /v1/delegation/chain/config. This ensures you have the latest contract addresses, especially after platform upgrades or network migrations.

Always verify contract addresses are correct before approving. Approving the wrong address could result in loss of funds.

Frontend Implementation

import { BrowserProvider, Contract, parseUnits } from 'ethers';

const ERC20_ABI = [
  'function approve(address spender, uint256 amount) returns (bool)',
  'function allowance(address owner, address spender) view returns (uint256)'
];

interface EVMDelegationParams {
  network: 'linea' | 'ethereum';
  currency: 'usdc' | 'usdt';
  amount: string;
  tokenAddress: string;
  spenderAddress: string;
  delegationToken: string;
}

async function delegateEVMWallet(
  params: EVMDelegationParams
): Promise<{
  address: string;
  network: string;
  currency: string;
  amount: string;
  txHash: string;
  sigHash: string;
  sigMessage: string;
  token: string;
}> {

  if (!window.ethereum) {
    throw new Error('No Ethereum wallet detected. Please install MetaMask.');
  }

  const provider = new BrowserProvider(window.ethereum);

  await provider.send('eth_requestAccounts', []);

  const network = await provider.getNetwork();
  const expectedChainId = params.network === 'linea' ? 59144n : 1n;

  if (network.chainId !== expectedChainId) {
    await switchNetwork(provider, params.network);
  }

  const signer = await provider.getSigner();
  const address = await signer.getAddress();

  console.log(`Connected wallet: ${address}`);

  const tokenContract = new Contract(
    params.tokenAddress,
    ERC20_ABI,
    signer
  );

  const decimals = params.currency === 'usdc' || params.currency === 'usdt' ? 6 : 18;
  const amountWei = parseUnits(params.amount, decimals);

  console.log(
    `Requesting approval for ${params.amount} ${params.currency.toUpperCase()} ` +
    `on ${params.network}`
  );

  const approveTx = await tokenContract.approve(
    params.spenderAddress,
    amountWei
  );

  console.log('Transaction submitted:', approveTx.hash);
  console.log('Waiting for confirmation...');

  const receipt = await approveTx.wait();

  if (!receipt || receipt.status !== 1) {
    throw new Error('Approval transaction failed');
  }

  console.log('Transaction confirmed in block:', receipt.blockNumber);

  const siweMessage = generateSIWEMessage(
    address,
    network.chainId.toString()
  );

  console.log('Requesting signature for proof...');
  const sigHash = await signer.signMessage(siweMessage);

  return {
    address,
    network: params.network,
    currency: params.currency,
    amount: params.amount,
    txHash: receipt.hash,
    sigHash,
    sigMessage: siweMessage,
    token: params.delegationToken
  };
}

async function switchNetwork(
  provider: BrowserProvider,
  network: 'linea' | 'ethereum'
) {
  const chainId = network === 'linea' ? '0xe708' : '0x1';

  try {
    await provider.send('wallet_switchEthereumChain', [{ chainId }]);
  } catch (error: any) {
    if (error.code === 4902) {
      if (network === 'linea') {
        await provider.send('wallet_addEthereumChain', [
          {
            chainId: '0xe708',
            chainName: 'Linea',
            nativeCurrency: {
              name: 'Ether',
              symbol: 'ETH',
              decimals: 18
            },
            rpcUrls: ['https://rpc.linea.build'],
            blockExplorerUrls: ['https://lineascan.build']
          }
        ]);
      } else {
        throw error;
      }
    } else {
      throw error;
    }
  }
}

function generateSIWEMessage(address: string, chainId: string): string {
  const domain = window.location.host;
  const nonce = generateNonce();
  const issuedAt = new Date().toISOString();
  const expirationTime = new Date(Date.now() + 30 * 60000).toISOString();

  return `${domain} wants you to sign in with your Ethereum account:
${address}

Prove wallet ownership for delegation

URI: https://${domain}
Version: 1
Chain ID: ${chainId}
Nonce: ${nonce}
Issued At: ${issuedAt}
Expiration Time: ${expirationTime}`;
}

function generateNonce(): string {
  return Math.random().toString(36).substring(2, 15) +
         Math.random().toString(36).substring(2, 15);
}

SIWE is the standard format for proving wallet ownership through message signing.

SIWE Message Format

{domain} wants you to sign in with your Ethereum account:
{address}

{statement}

URI: {uri}
Version: {version}
Chain ID: {chainId}
Nonce: {nonce}
Issued At: {issuedAt}
Expiration Time: {expirationTime}

Field Descriptions

Field	Required	Description	Example
`domain`	Yes	Domain requesting signature	`yourplatform.com`
`address`	Yes	User’s Ethereum address	`0x3a11a86cf...`
`statement`	No	Human-readable statement	`Prove wallet ownership for delegation`
`uri`	Yes	Full URI of requesting application	`https://yourplatform.com`
`version`	Yes	SIWE version (always “1”)	`1`
`chainId`	Yes	Blockchain chain ID	`59144` (Linea) or `1` (Ethereum)
`nonce`	Yes	Random string to prevent replay attacks	`abc123xyz789`
`issuedAt`	Yes	ISO 8601 timestamp	`2024-10-08T12:00:00Z`
`expirationTime`	No	ISO 8601 timestamp when signature expires	`2024-10-08T12:30:00Z`

The SIWE message format must be exact. Extra whitespace, missing fields, or incorrect formatting will cause signature verification to fail.

SIWE Implementation

function generateSIWEMessage(
  address: string,
  chainId: string,
  domain: string = window.location.host
): string {
  const nonce = crypto.randomUUID().replace(/-/g, '');
  const issuedAt = new Date().toISOString();
  const expirationTime = new Date(Date.now() + 30 * 60000).toISOString();

  return `${domain} wants you to sign in with your Ethereum account:
${address}

Prove wallet ownership for delegation

URI: https://${domain}
Version: 1
Chain ID: ${chainId}
Nonce: ${nonce}
Issued At: ${issuedAt}
Expiration Time: ${expirationTime}`;
}

Gas Optimization

Check Existing Allowance

Before requesting a new approval, check if sufficient allowance already exists:

async function checkAllowance(
  tokenAddress: string,
  ownerAddress: string,
  spenderAddress: string
): Promise<bigint> {
  const provider = new BrowserProvider(window.ethereum);

  const tokenContract = new Contract(
    tokenAddress,
    ['function allowance(address owner, address spender) view returns (uint256)'],
    provider
  );

  const allowance = await tokenContract.allowance(ownerAddress, spenderAddress);
  return allowance;
}

async function requestApprovalIfNeeded(
  tokenAddress: string,
  spenderAddress: string,
  amount: string
): Promise<string | null> {
  const provider = new BrowserProvider(window.ethereum);
  const signer = await provider.getSigner();
  const address = await signer.getAddress();

  const existingAllowance = await checkAllowance(
    tokenAddress,
    address,
    spenderAddress
  );

  const requiredAmount = parseUnits(amount, 6);

  if (existingAllowance >= requiredAmount) {
    console.log('Sufficient allowance already exists');
    return null; // No new transaction needed
  }

  const tokenContract = new Contract(tokenAddress, ERC20_ABI, signer);
  const tx = await tokenContract.approve(spenderAddress, requiredAmount);
  const receipt = await tx.wait();

  return receipt.hash;
}

Gas Price Strategies

Standard
Custom Gas Price
Gas Estimation

Let wallet handle gas price estimation (recommended):

const tx = await tokenContract.approve(spender, amount);
// Wallet will estimate gas automatically

Set custom gas parameters for faster confirmation:

const feeData = await provider.getFeeData();

const tx = await tokenContract.approve(spender, amount, {
  maxFeePerGas: feeData.maxFeePerGas! * 120n / 100n, // 20% higher
  maxPriorityFeePerGas: feeData.maxPriorityFeePerGas! * 120n / 100n
});

Estimate gas before sending:

const gasEstimate = await tokenContract.approve.estimateGas(
  spender,
  amount
);

console.log(`Estimated gas: ${gasEstimate.toString()}`);

const tx = await tokenContract.approve(spender, amount, {
  gasLimit: gasEstimate * 120n / 100n // 20% buffer
});

Submit to API

After collecting all data from the blockchain, submit to the EVM-specific endpoint:

API Request

interface EVMDelegationProof {
  address: string;          // Must start with 0x, 42 characters total
  network: 'linea' | 'ethereum';
  currency: 'usdc' | 'usdt';
  amount: string;
  txHash: string;           // Must start with 0x, 66 characters total
  sigHash: string;          // Must start with 0x, 132 characters total
  sigMessage: string;       // SIWE formatted message
  token: string;            // From Step 1
}

async function submitEVMDelegation(
  proof: EVMDelegationProof,
  userAccessToken: string
): Promise<boolean> {
  const response = await fetch(
    'https://api.yourplatform.com/v1/delegation/evm/post-approval',
    {
      method: 'POST',
      headers: {
        'x-client-key': process.env.CLIENT_PUBLIC_KEY!,
        'Authorization': `Bearer ${userAccessToken}`,
        'Content-Type': 'application/json'
      },
      body: JSON.stringify(proof)
    }
  );

  if (!response.ok) {
    const error = await response.json();
    throw new Error(error.message || 'Delegation failed');
  }

  const data = await response.json();
  return data.success;
}

API Reference: POST /v1/delegation/evm/post-approval

Validation Rules

The API performs strict EVM-specific validation:

Address Format

Must start with 0x
Must be exactly 42 characters long
Must contain only hexadecimal characters (0-9, a-f)
Case-insensitive, but checksummed addresses are preferred

Valid: 0x3a11a86cf218c448be519728cd3ac5c741fb3424 Invalid: 3a11a86cf218c448be519728cd3ac5c741fb3424 (missing 0x)

Transaction Hash

Must start with 0x
Must be exactly 66 characters long
Must contain only hexadecimal characters
Must be a confirmed transaction on the specified network

Valid: 0xb92de09d893e8162b0861c0f7321f68df02212efbc58f208839ae3f176d89638

Signature Hash

Must start with 0x
Must be exactly 132 characters long
Must contain only hexadecimal characters
Must be valid ECDSA signature that recovers to the provided address

Valid: 0x2039b9765a4df76e8bae80f3bbc640e8ae6acc81f7a5cc96fe91ccc1844b6f7d4c3e8f1a2b...

SIWE Message

Must follow SIWE format exactly
Must contain the provided address
Must contain correct chain ID for network
Must not be expired (check expirationTime if present)

Error Handling

Common EVM Errors

async function handleEVMDelegation() {
  try {
    await delegateEVMWallet(params);
  } catch (error: any) {
    if (error.code === 4001) {
      console.error('User rejected transaction');
      alert('Please approve the transaction in your wallet to continue');
    }
    else if (error.code === -32603) {
      console.error('Insufficient funds for gas');
      alert('You need more ETH in your wallet to pay for gas fees');
    }
    else if (error.message?.includes('wrong network')) {
      console.error('Wrong network');
      alert('Please switch to the correct network in your wallet');
    }
    else if (error.message?.includes('insufficient allowance')) {
      console.error('Approval failed or insufficient');
      alert('Please try approving the transaction again');
    }
    else if (error.code === -32002) {
      console.error('Request already pending');
      alert('Please check your wallet for a pending request');
    }
    else {
      console.error('Unknown error:', error);
      alert(`Delegation failed: ${error.message}`);
    }
  }
}

API Error Responses

Status	Error	Cause	Solution
400	Invalid address format	Address doesn’t match EVM format	Ensure address starts with 0x and is 42 chars
400	Invalid transaction hash	Transaction hash not found or wrong format	Wait for confirmation, verify network
400	Invalid signature	Signature doesn’t match address	Re-sign message, ensure correct wallet
400	Expired token	Delegation token expired	Generate new token from Step 1
400	SIWE validation failed	Message format incorrect	Use exact SIWE format
429	Rate limited	Too many requests	Wait and retry with exponential backoff

Testing

Test on Linea Testnet

Before going to production, test on Linea Goerli testnet:

const TESTNET_CONFIG = {
  chainId: 59140, // Linea Goerli
  chainIdHex: '0xe704',
  rpcUrl: 'https://rpc.goerli.linea.build',
  blockExplorer: 'https://goerli.lineascan.build',
  nativeCurrency: {
    name: 'Ether',
    symbol: 'ETH',
    decimals: 18
  }
};

async function addLineaTestnet() {
  await window.ethereum.request({
    method: 'wallet_addEthereumChain',
    params: [{
      chainId: TESTNET_CONFIG.chainIdHex,
      chainName: 'Linea Goerli',
      nativeCurrency: TESTNET_CONFIG.nativeCurrency,
      rpcUrls: [TESTNET_CONFIG.rpcUrl],
      blockExplorerUrls: [TESTNET_CONFIG.blockExplorer]
    }]
  });
}

Get testnet ETH from:

Linea Goerli Faucet: https://faucet.goerli.linea.build
Goerli ETH Faucet: https://goerlifaucet.com

Next Steps

Solana Implementation

Learn how delegation works on Solana

Priority Management

Configure wallet charging priority

Redelegation

Update allowances and contracts

Implementation Guide

Complete 3-step delegation workflow

Getting Started

OAuth 2.0 & Authentication

User Management

Wallet Management

Non-Custodial Wallet Delegation

Card Operations

Overview

Supported EVM Networks

ERC20 Approval Pattern

The approve() Function

How It Works

Implementation

Contract Addresses

Frontend Implementation

SIWE Message Format

Field Descriptions

SIWE Implementation

Gas Optimization

Check Existing Allowance

Gas Price Strategies

Submit to API

API Request

Validation Rules

Error Handling

Common EVM Errors

API Error Responses

Testing

Test on Linea Testnet

Next Steps

Solana Implementation

Priority Management

Redelegation

Implementation Guide

Getting Started

OAuth 2.0 & Authentication

User Management

Wallet Management

Non-Custodial Wallet Delegation

Card Operations

​Overview

​Supported EVM Networks

​ERC20 Approval Pattern

​The approve() Function

​How It Works

​Implementation

​Contract Addresses

​Frontend Implementation

​SIWE (Sign-In with Ethereum)

​SIWE Message Format

​Field Descriptions

​SIWE Implementation

​Gas Optimization

​Check Existing Allowance

​Gas Price Strategies

​Submit to API

​API Request

​Validation Rules

​Error Handling

​Common EVM Errors

​API Error Responses

​Testing

​Test on Linea Testnet

​Next Steps

Solana Implementation

Priority Management

Redelegation

Implementation Guide

Overview

Supported EVM Networks

ERC20 Approval Pattern

The approve() Function

How It Works

Implementation

Contract Addresses

Frontend Implementation

SIWE (Sign-In with Ethereum)

SIWE Message Format

Field Descriptions

SIWE Implementation

Gas Optimization

Check Existing Allowance

Gas Price Strategies

Submit to API

API Request

Validation Rules

Error Handling

Common EVM Errors

API Error Responses

Testing

Test on Linea Testnet

Next Steps