Function Signature 
swiftCopypublic func buildEip155Transaction(
    chainId: String,
    params: BuildTransactionParam
) async throws -> BuildEip115TransactionResponse
Parameters
  1. chainId: The chain identifier in CAIP-2 format (e.g., “eip155:1” for Ethereum mainnet)
  2. params: A BuildTransactionParam object containing:
    • to: Recipient’s address
    • token: Token identifier or contract address
    • amount: Amount to transfer as a string
Returns A BuildEip115TransactionResponse containing:
  • transaction: An Eip115Transaction object with:
    • from: Sender’s address
    • to: Recipient’s address
    • data: Optional transaction data for contract interactions
    • value: Optional transaction value in wei
  • metadata: A BuildTransactionMetaData object containing:
    • amount: Formatted transaction amount
    • fromAddress: Sender’s address
    • toAddress: Recipient’s address
    • tokenAddress: Optional token contract address for ERC20 transfers
    • tokenDecimals: Number of decimal places for the token
    • tokenSymbol: Optional token symbol
    • rawAmount: Raw transaction amount value
  • error: Optional error message if the build process encounters issues
Example Usage 
// Native ETH transfer
do {
    let params = BuildTransactionParam(
        to: "0x1234567890123456789012345678901234567890",
        token: "ETH",
        amount: "1000000000000000000" // 1 ETH
    )

    let response = try await portal.buildEip155Transaction(
        chainId: "eip155:1",
        params: params
    )

    print("Transaction details:")
    print("From: \(response.transaction.from)")
    print("To: \(response.transaction.to)")
    print("Value: \(response.transaction.value ?? "0")")

    print("\nMetadata:")
    print("Amount: \(response.metadata.amount)")
    print("Token Symbol: \(response.metadata.tokenSymbol ?? "ETH")")

    if let error = response.error {
        print("Warning: \(error)")
    }
} catch {
    print("Failed to build transaction: \(error)")
}

// ERC20 token transfer
do {
    // Example: Transfer 100 USDC
    let params = BuildTransactionParam(
        to: "0x1234567890123456789012345678901234567890",
        token: "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48", // USDC contract address
        amount: "100000000" // 100 USDC (6 decimals)
    )

    let response = try await portal.buildEip155Transaction(
        chainId: "eip155:1",
        params: params
    )

    // Verify the built transaction
    print("Token Transfer Details:")
    print("Contract Address: \(response.metadata.tokenAddress ?? "N/A")")
    print("Amount: \(response.metadata.amount) \(response.metadata.tokenSymbol ?? "tokens")")
    print("From: \(response.metadata.fromAddress)")
    print("To: \(response.metadata.toAddress)")
    print("Raw Amount: \(response.metadata.rawAmount)")
} catch {
    print("Failed to build token transfer: \(error)")
}

// Example with transaction validation
func buildAndValidateTransaction(
    to: String,
    token: String,
    amount: String
) async throws {
    // Build the transaction
    let params = BuildTransactionParam(
        to: to,
        token: token,
        amount: amount
    )

    let response = try await portal.buildEip155Transaction(
        chainId: "eip155:1",
        params: params
    )

    // Validate the response
    guard response.error == nil else {
        throw TransactionError.buildFailed(response.error!)
    }

    // Validate addresses
    guard response.metadata.fromAddress.starts(with: "0x"),
          response.metadata.toAddress.starts(with: "0x") else {
        throw TransactionError.invalidAddress
    }

    // Validate amount
    guard let rawAmount = Double(response.metadata.rawAmount),
          rawAmount > 0 else {
        throw TransactionError.invalidAmount
    }

    print("Transaction validated successfully")
    print("Ready to send: \(response.metadata.amount) \(response.metadata.tokenSymbol ?? "tokens")")
}
Implementation Notes
  1. Transaction Types:
    • For native ETH transfers, use “ETH” as the token identifier
    • For ERC20 transfers, use the token’s contract address as the token identifier
    • Amount should be provided in the token’s smallest unit (wei for ETH, token-specific decimal places for ERC20)
  2. Token Handling:
    • Native ETH is identified by “ETH” token value
    • ERC20 tokens are identified by their contract address
    • Amount decimal places must match the token’s decimal configuration
  3. Amount Formats:
    • ETH amounts should be in wei (1 ETH = 1e18 wei)
    • Token amounts should account for the token’s decimal places
    • All amounts should be provided as strings to preserve precision
  4. Error Handling:
    • Check response.error for build-specific issues
    • Validate addresses are in correct Ethereum format
    • Verify amount format matches token decimals
    • Handle network-specific errors during transaction building
Related Documentation For more information about transaction building, see: