Batch transfers using smart contracts

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A batch transfer smart contract allows you to execute multiple token transfers in a single on-chain transaction, making it suitable for scenarios such as batch payouts or batch withdrawals. Compared to repeatedly calling the transfer API, the batch method reduces the need for multiple signatures and requests, improving operational efficiency. This guide explains how to use the Call smart contract API to invoke the batch transfer smart contract deployed by Cobo, enabling batch token transfers.

The transaction fee for batch transfers using the smart contract API may not necessarily be lower than the total fee for multiple individual transfer token API calls. The actual cost depends on the on-chain gas price and the number of transfers; with a small number of recipients, batch transfers could even be more expensive. We recommend using the Estimate transaction fee API to compare the cost of both approaches before initiating a transfer.

Supported chains

The following EVM-compatible chains are supported:

Ethereum Mainnet
BNB Smart Chain
Base Mainnet
Arbitrum One
Polygon PoS

The address of the batch transfer smart contract is 0x3d963e23a9229D2ACd25E9FFC358be1a35460ecc

Prerequisites

You have set up Cobo Accounts and successfully sent requests as described in Send your first API request.
You are familiar with and able to use the Call smart contract API.
You have basic knowledge of interacting with smart contracts, including preparing calldata, locating contract methods, and using the approve method on a token contract to authorize the batch transfer contract to spend tokens.
The batch transfer feature currently only supports transactions initiated from MPC Wallets and Custodial Wallets (Web3 Wallets).

Batch transfer of ETH

The following steps apply to batch transfers of ETH (native coin) on the supported chains:

Prepare parameters
- Use the sendEther method to generate calldata (either with Cobo’s script or your own tool).
  When generating calldata, provide:
  - recipients (address[]): array of recipient addresses.
  - values (uint256[]): array of amounts for each address (in wei).
- The number of recipients must not exceed 200 (recipients array length ≤ 200).
Call the Call smart contract API
- Specify the batch transfer contract address: 0x3d963e23a9229D2ACd25E9FFC358be1a35460ecc
- Provide the generated calldata.
- The value in the API request must equal the sum of all values in the values array in the calldata.
Wait for confirmation and check results
- Use the returned tx_hash to check the transaction status.
- In Cobo Portal’s transaction history, you will see a transaction of the contract call type.
- If any recipient address belongs to a Cobo Account, the corresponding organization will also see a transaction of the deposit type.

Batch transfer of other tokens

The following steps apply to batch transfers of ERC-20 tokens on the supported chains:

Call the token contract’s approve method
- Each token has its own contract address, so run approve on the specific token’s contract.
- Approve the source address (the one specified in the source field of the smart contract call request).
- The approved amount must be greater than or equal to the total transfer amount.
  Before calling the batch transfer contract, use an on-chain query or API request to confirm that the approve transaction has been successfully confirmed and completed.
Prepare parameters
- Use the sendToken method to generate calldata (either with Cobo’s script or your own tool).
  When generating calldata, provide:
  - token (address): ERC-20 token contract address.
  - recipients (address[]): array of recipient addresses.
  - values (uint256[]): array of amounts for each address (in the token’s smallest unit).
- The number of recipients must not exceed 200 (recipients array length ≤ 200).
Call the Call smart contract API
- Specify the batch transfer contract address: 0x3d963e23a9229D2ACd25E9FFC358be1a35460ecc
- Provide the generated calldata.
- Set value to 0 when making the API call.
Wait for confirmation and check results
- Use the returned tx_hash to check the transaction status.
- In Cobo Portal’s transaction history, you will see a transaction of the contract call type.
- If any recipient address belongs to a Cobo Account, the corresponding organization will also see a transaction of the deposit type.

Additional notes

You can use Fee Station to pay on-chain transaction fees with gas tokens or USD stablecoins.
You can also manually call the batch transfer smart contract with the “Write Contract” function on a blockchain explorer. This method requires connecting your MPC Wallet or Custodial Wallet (Web3 Wallet) using a supported browser extension (such as Cobo Connect), without using API calls.

Common failure causes

Insufficient balance or insufficient approval amount.
Mismatch between the length of recipients and the length of the amount array.
Number of recipients exceeds the limit.
Mismatch between the value in the API request and the amounts in the calldata (for ETH transfers).
Insufficient gas limit.

Example script for generating `calldata`

The following is a Python script provided by Cobo to generate calldata. You can also generate on your own.

# !/usr/bin/env python3
"""
Contract Call Data Generator

This script generates call data for the provided smart contract ABI.
It supports all functions defined in the ABI including multicall, send, sendEther, sendToken, etc.
"""

import json
from web3 import Web3
from typing import List, Optional, Union
from eth_utils import to_checksum_address


class ContractCallDataGenerator:
    def __init__(self, abi_json: str):
        """
        Initialize the generator with contract ABI

        Args:
            abi_json (str): JSON string of the contract ABI
        """
        self.abi = json.loads(abi_json)
        self.w3 = Web3()
        self.contract = self.w3.eth.contract(abi=self.abi)

    def get_eth_address_calldata(self) -> str:
        """Generate calldata for ETH_ADDRESS() function"""
        return self.contract.encodeABI(fn_name='ETH_ADDRESS')

    def get_owner_calldata(self) -> str:
        """Generate calldata for owner() function"""
        return self.contract.encodeABI(fn_name='owner')

    def get_renounce_ownership_calldata(self) -> str:
        """Generate calldata for renounceOwnership() function"""
        return self.contract.encodeABI(fn_name='renounceOwnership')

    def get_transfer_ownership_calldata(self, new_owner: str) -> str:
        """
        Generate calldata for transferOwnership(address newOwner) function

        Args:
            new_owner (str): New owner address
        """
        new_owner = to_checksum_address(new_owner)
        return self.contract.encodeABI(
            fn_name='transferOwnership',
            args=[new_owner]
        )

    def get_rescue_calldata(self, token: str, amount: int) -> str:
        """
        Generate calldata for rescue(address _token, uint256 _amount) function

        Args:
            token (str): Token contract address
            amount (int): Amount to rescue
        """
        token = to_checksum_address(token)
        return self.contract.encodeABI(
            fn_name='rescue',
            args=[token, amount]
        )

    def get_multicall_calldata(self, data: List[bytes]) -> str:
        """
        Generate calldata for multicall(bytes[] data) function

        Args:
            data (List[bytes]): List of encoded function calls
        """
        return self.contract.encodeABI(
            fn_name='multicall',
            args=[data]
        )

    def get_send_ether_calldata(self, recipients: List[str], values: List[int]) -> str:
        """
        Generate calldata for sendEther(address[] recipients, uint256[] values) function

        Args:
            recipients (List[str]): List of recipient addresses
            values (List[int]): List of values to send
        """
        recipients = [to_checksum_address(addr) for addr in recipients]
        return self.contract.encodeABI(
            fn_name='sendEther',
            args=[recipients, values]
        )

    def get_send_token_calldata(self, token: str, recipients: List[str], values: List[int]) -> str:
        """
        Generate calldata for sendToken(contract IERC20 token, address[] recipients, uint256[] values) function

        Args:
            token (str): Token contract address
            recipients (List[str]): List of recipient addresses
            values (List[int]): List of values to send
        """
        token = to_checksum_address(token)
        recipients = [to_checksum_address(addr) for addr in recipients]
        return self.contract.encodeABI(
            fn_name='sendToken',
            args=[token, recipients, values]
        )

    def get_send_calldata(self, tokens: List[str], recipients: List[str], values: List[int]) -> str:
        """
        Generate calldata for send(address[] tokens, address[] recipients, uint256[] values) function

        Args:
            tokens (List[str]): List of token addresses
            recipients (List[str]): List of recipient addresses
            values (List[int]): List of values to send
        """
        tokens = [to_checksum_address(addr) for addr in tokens]
        recipients = [to_checksum_address(addr) for addr in recipients]
        return self.contract.encodeABI(
            fn_name='send',
            args=[tokens, recipients, values]
        )


def main():
    """Main function with usage examples"""

    # Contract ABI
    abi_json = '''[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[{"internalType":"address","name":"target","type":"address"}],"name":"AddressEmptyCode","type":"error"},{"inputs":[],"name":"FailedCall","type":"error"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"OwnableInvalidOwner","type":"error"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"OwnableUnauthorizedAccount","type":"error"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"SafeERC20FailedOperation","type":"error"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"inputs":[],"name":"ETH_ADDRESS","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes[]","name":"data","type":"bytes[]"}],"name":"multicall","outputs":[{"internalType":"bytes[]","name":"results","type":"bytes[]"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"owner","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"renounceOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"_token","type":"address"},{"internalType":"uint256","name":"_amount","type":"uint256"}],"name":"rescue","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address[]","name":"tokens","type":"address[]"},{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"send","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"sendEther","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"contract IERC20","name":"token","type":"address"},{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"sendToken","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"}]'''

    # Initialize generator
    generator = ContractCallDataGenerator(abi_json)

    print("=== Contract Call Data Generator ===\n")

    # Example 1: Get ETH_ADDRESS calldata
    eth_address_calldata = generator.get_eth_address_calldata()
    print(f"ETH_ADDRESS() calldata: {eth_address_calldata}")

    # Example 2: Get owner calldata
    owner_calldata = generator.get_owner_calldata()
    print(f"owner() calldata: {owner_calldata}")

    # Example 3: Transfer ownership
    new_owner = "0x44E734ad441C190EDf58E912b58AA6373AB945f8"
    transfer_ownership_calldata = generator.get_transfer_ownership_calldata(new_owner)
    print(f"transferOwnership(address) calldata: {transfer_ownership_calldata}")

    # Example 4: Rescue tokens
    token_address = "0x8d89ca14bcd4107843c62015ba332150e5f11013"
    amount = 2 # 1 token (assuming 18 decimals)
    rescue_calldata = generator.get_rescue_calldata(token_address, amount)
    print(f"rescue(address, uint256) calldata: {rescue_calldata}")

    # Example 5: Send Ether to multiple recipients
    recipients = ["0x3573c0923aecc5bfdcbd3ffd022be96550a23fb4","0xe389b99f5b4bbbcd5247b19e953e4ff86b961ae4"]
    # recipients = [
    #               "0x250d3aa593f0db4588f400ee74b09f20e6fb47af",
    #               "0x5d14046ccc418d41004527b091bce7de4eefde1e",
    #               "0x91e1d5bcd9f919f7a1a541c9fed150de4cdd6720",
    #               "0x5218bc8a3cbd5d65e10095c2573f8b0b5ff1f6eb",
    #               ]

    # values = [1,1]
    values = [1, 1]
    send_ether_calldata = generator.get_send_ether_calldata(recipients, values)
    print(f"sendEther(address[], uint256[]) calldata: {send_ether_calldata}")

    # Example 6: Send tokens to multiple recipients
    # token_contract = "0xA0b86991c6218b36c1d19D4a2e9Eb0cE3606eB48"
    token_contract = "0x8d89ca14bcd4107843c62015ba332150e5f11013"
    token_values = [4,5]
     # 0.5 tokens, 1.5 tokens
    send_token_calldata = generator.get_send_token_calldata(token_contract, recipients, token_values)
    print(f"sendToken(address, address[], uint256[]) calldata: {send_token_calldata}")

    # Example 7: Multi-send (different tokens to different recipients)
    tokens = [
        "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE",  # ETH
        "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE",  # ETH
        "0x8d89ca14bcd4107843c62015ba332150e5f11013", # Token
        "0x8d89ca14bcd4107843c62015ba332150e5f11013"
    ]
    # tokens = ["0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE", "0xEeeeeEeeeEeEeeEeEeEeeEEEeeeeEeeeeeeeEEeE"]

    send_calldata = generator.get_send_calldata(tokens, recipients, values)
    print(f"send(address[], address[], uint256[]) calldata: {send_calldata}")

    # Example 8: Multicall - combining multiple operations
    # First, prepare individual call data
    call1 = generator.get_owner_calldata()
    call2 = generator.get_eth_address_calldata()


    # Convert hex strings to bytes
    call_data = [ bytes.fromhex(send_token_calldata[2:])]
    multicall_calldata = generator.get_multicall_calldata(call_data)
    print(f"multicall(bytes[]) calldata: {multicall_calldata}")

    # Example 9: Renounce ownership
    renounce_calldata = generator.get_renounce_ownership_calldata()
    print(f"renounceOwnership() calldata: {renounce_calldata}")

    print("\n=== Usage Instructions ===")
    print("1. Install required packages: pip install web3 eth-utils")
    print("2. Use the generated calldata in your transaction")
    print("3. Set appropriate gas limits for each function")
    print("4. For payable functions (send, sendEther), include ETH value in transaction")


def interactive_mode():
    """Interactive mode for custom calldata generation"""
    abi_json = '''[{"inputs":[],"stateMutability":"nonpayable","type":"constructor"},{"inputs":[{"internalType":"address","name":"target","type":"address"}],"name":"AddressEmptyCode","type":"error"},{"inputs":[],"name":"FailedCall","type":"error"},{"inputs":[{"internalType":"address","name":"owner","type":"address"}],"name":"OwnableInvalidOwner","type":"error"},{"inputs":[{"internalType":"address","name":"account","type":"address"}],"name":"OwnableUnauthorizedAccount","type":"error"},{"inputs":[{"internalType":"address","name":"token","type":"address"}],"name":"SafeERC20FailedOperation","type":"error"},{"anonymous":false,"inputs":[{"indexed":true,"internalType":"address","name":"previousOwner","type":"address"},{"indexed":true,"internalType":"address","name":"newOwner","type":"address"}],"name":"OwnershipTransferred","type":"event"},{"inputs":[],"name":"ETH_ADDRESS","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[{"internalType":"bytes[]","name":"data","type":"bytes[]"}],"name":"multicall","outputs":[{"internalType":"bytes[]","name":"results","type":"bytes[]"}],"stateMutability":"nonpayable","type":"function"},{"inputs":[],"name":"owner","outputs":[{"internalType":"address","name":"","type":"address"}],"stateMutability":"view","type":"function"},{"inputs":[],"name":"renounceOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"_token","type":"address"},{"internalType":"uint256","name":"_amount","type":"uint256"}],"name":"rescue","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address[]","name":"tokens","type":"address[]"},{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"send","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"sendEther","outputs":[],"stateMutability":"payable","type":"function"},{"inputs":[{"internalType":"contract IERC20","name":"token","type":"address"},{"internalType":"address[]","name":"recipients","type":"address[]"},{"internalType":"uint256[]","name":"values","type":"uint256[]"}],"name":"sendToken","outputs":[],"stateMutability":"nonpayable","type":"function"},{"inputs":[{"internalType":"address","name":"newOwner","type":"address"}],"name":"transferOwnership","outputs":[],"stateMutability":"nonpayable","type":"function"}]'''

    generator = ContractCallDataGenerator(abi_json)

    print("=== Interactive Call Data Generator ===")
    print("Available functions:")
    print("1. ETH_ADDRESS()")
    print("2. owner()")
    print("3. renounceOwnership()")
    print("4. transferOwnership(address)")
    print("5. rescue(address, uint256)")
    print("6. sendEther(address[], uint256[])")
    print("7. sendToken(address, address[], uint256[])")
    print("8. send(address[], address[], uint256[])")
    print("9. multicall(bytes[])")
    print("0. Exit")

    while True:
        try:
            choice = input("\nEnter function number (0-9): ")

            if choice == '0':
                break
            elif choice == '1':
                print(f"Calldata: {generator.get_eth_address_calldata()}")
            elif choice == '2':
                print(f"Calldata: {generator.get_owner_calldata()}")
            elif choice == '3':
                print(f"Calldata: {generator.get_renounce_ownership_calldata()}")
            elif choice == '4':
                new_owner = input("Enter new owner address: ")
                print(f"Calldata: {generator.get_transfer_ownership_calldata(new_owner)}")
            elif choice == '5':
                token = input("Enter token address: ")
                amount = int(input("Enter amount: "))
                print(f"Calldata: {generator.get_rescue_calldata(token, amount)}")
            elif choice == '6':
                recipients = input("Enter recipient addresses (comma-separated): ").split(',')
                values = [int(x) for x in input("Enter values (comma-separated): ").split(',')]
                print(f"Calldata: {generator.get_send_ether_calldata(recipients, values)}")
            elif choice == '7':
                token = input("Enter token address: ")
                recipients = input("Enter recipient addresses (comma-separated): ").split(',')
                values = [int(x) for x in input("Enter values (comma-separated): ").split(',')]
                print(f"Calldata: {generator.get_send_token_calldata(token, recipients, values)}")
            elif choice == '8':
                tokens = input("Enter token addresses (comma-separated): ").split(',')
                recipients = input("Enter recipient addresses (comma-separated): ").split(',')
                values = [int(x) for x in input("Enter values (comma-separated): ").split(',')]
                print(f"Calldata: {generator.get_send_calldata(tokens, recipients, values)}")
            else:
                print("Invalid choice. Please try again.")

        except Exception as e:
            print(f"Error: {e}")


if __name__ == "__main__":
    # Run main examples
    main()

    # Optionally run interactive mode
    # run_interactive = input("\nRun interactive mode? (y/n): ")
    # if run_interactive.lower() == 'y':
    #     interactive_mode()

​Supported chains

​Prerequisites

​Batch transfer of ETH

​Batch transfer of other tokens

​Additional notes

​Common failure causes

​Example script for generating calldata

Supported chains

Prerequisites

Batch transfer of ETH

Batch transfer of other tokens

Additional notes

Common failure causes

Example script for generating `calldata`