buildEip155Transaction

Function Signature

Future<PortalBuildEip155TransactionResponse> buildEip155Transaction({
  required String chainId,
  required String to,
  required String token,
  required String amount,
})

Description

Builds an unsigned EIP-155 transaction via the Portal backend. The returned payload is ready to be signed and submitted using portal.request(method: 'eth_sendTransaction', ...).

Parameters

Parameter	Type	Required	Description
`chainId`	`String`	Yes	The chain ID in CAIP-2 format. Must start with `eip155:` (e.g. `eip155:1` for mainnet, `eip155:11155111` for Sepolia).
`to`	`String`	Yes	The recipient address (`0x…`).
`token`	`String`	Yes	The asset symbol (e.g. `ETH`) for native transfers, or the ERC-20 token contract address.
`amount`	`String`	Yes	The human-readable amount (e.g. `"0.001"`, `"100"`). The backend converts this to the token’s smallest unit.

Returns

PortalBuildEip155TransactionResponse — the unsigned transaction plus metadata.

Property	Type	Description
`transaction`	`PortalEip155Transaction`	The unsigned transaction payload to pass to `eth_sendTransaction`.
`metadata`	`PortalBuildTransactionMetadata`	Token info, formatted amounts, and the resolved sender / recipient addresses.
`error`	`String?`	Optional backend error message. Inspect this before submitting the transaction.

PortalEip155Transaction

Property	Type	Description
`from`	`String`	The sender address (the Portal wallet’s EVM address).
`to`	`String`	The destination address.
`data`	`String?`	Optional hex-encoded calldata (populated for ERC-20 transfers).
`value`	`String?`	Optional hex-encoded value in wei (populated for native transfers).

PortalBuildTransactionMetadata

Property	Type	Description
`amount`	`String`	Formatted (human-readable) amount.
`fromAddress`	`String`	Sender address.
`toAddress`	`String`	Recipient address.
`tokenAddress`	`String?`	ERC-20 contract address (null for native transfers).
`tokenDecimals`	`int`	Token decimals.
`tokenSymbol`	`String?`	Token symbol when known.
`rawAmount`	`String`	Amount in the token’s smallest unit (wei for native ETH).

Examples

Native ETH transfer

import 'package:portal_flutter/portal_flutter.dart';

final portal = Portal();

final response = await portal.buildEip155Transaction(
  chainId: 'eip155:11155111', // Sepolia
  to: '0x1234567890123456789012345678901234567890',
  token: 'ETH',
  amount: '0.001',
);

if (response.error != null) {
  throw Exception('Failed to build transaction: ${response.error}');
}

final symbol = response.metadata.tokenSymbol ?? 'ETH';
print('From: ${response.transaction.from}');
print('To: ${response.transaction.to}');
print('Value (wei): ${response.transaction.value}');
print('Amount: ${response.metadata.amount} $symbol');

ERC-20 token transfer

final response = await portal.buildEip155Transaction(
  chainId: 'eip155:1',
  to: '0x1234567890123456789012345678901234567890',
  token: '0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48', // USDC
  amount: '100',
);

final symbol = response.metadata.tokenSymbol ?? 'Unknown';
print('Token: $symbol');
print('Token contract: ${response.metadata.tokenAddress}');
print('Calldata: ${response.transaction.data}');
print('Raw amount: ${response.metadata.rawAmount}');

Build, then sign and submit

buildEip155Transaction only constructs the transaction — pass the result to request to actually sign and broadcast it:

final built = await portal.buildEip155Transaction(
  chainId: 'eip155:1',
  to: recipient,
  token: 'ETH',
  amount: '0.01',
);

if (built.error != null) {
  throw Exception(built.error);
}

final txResponse = await portal.request(
  chainId: 'eip155:1',
  method: 'eth_sendTransaction',
  params: [
    {
      'from': built.transaction.from,
      'to': built.transaction.to,
      if (built.transaction.value != null) 'value': built.transaction.value,
      if (built.transaction.data != null) 'data': built.transaction.data,
    },
  ],
);

// portal.request returns a PortalProviderResponse with String? result + String? error.
if (txResponse.error != null) {
  throw Exception('eth_sendTransaction failed: ${txResponse.error}');
}

print('Transaction hash: ${txResponse.result}');

Errors

Throws a PortalException on failure:

Code	Description
`NOT_INITIALIZED`	Portal was not initialized.
`BUILD_FAILED`	The backend could not build the transaction (insufficient funds, unsupported token, invalid recipient).

try {
  final response = await portal.buildEip155Transaction(
    chainId: 'eip155:1',
    to: recipient,
    token: 'ETH',
    amount: '0.01',
  );
} on PortalException catch (e) {
  print('Build failed: ${e.code} - ${e.message}');
}

Always also check response.error — the backend may signal a soft failure (e.g. a non-fatal warning about insufficient balance) without throwing.

Implementation Notes

amount is the human-readable value. The Portal backend handles decimal conversion based on the token. Pass "0.001" for 0.001 ETH, not "1000000000000000".
For native transfers, use the symbol "ETH" (or the chain’s native symbol). For tokens, use the contract address.
chainId must start with eip155:. Use buildSolanaTransaction for Solana.

Getting Started

SDKs

APIs

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Resources

buildEip155Transaction

Function Signature

Description

Parameters

Returns

PortalEip155Transaction

PortalBuildTransactionMetadata

Examples

Native ETH transfer

ERC-20 token transfer

Build, then sign and submit

Errors

Implementation Notes

​Function Signature

​Description

​Parameters

​Returns

​PortalEip155Transaction

​PortalBuildTransactionMetadata

​Examples

​Native ETH transfer

​ERC-20 token transfer

​Build, then sign and submit

​Errors

​Implementation Notes

​Related

Function Signature

Description

Parameters

Returns

PortalEip155Transaction

PortalBuildTransactionMetadata

Examples

Native ETH transfer

ERC-20 token transfer

Build, then sign and submit

Errors

Implementation Notes

Related