class Eth::Client

def transfer(destination, amount, sender_key = nil, legacy = false)
  params = {
    value: amount,
    to: destination,
    gas_limit: gas_limit,
    chain_id: chain_id,
  }
  if legacy
    params.merge!({
      gas_price: max_fee_per_gas,
    })
  else
    params.merge!({
      priority_fee: max_priority_fee_per_gas,
      max_gas_fee: max_fee_per_gas,
    })
  end
  unless sender_key.nil?
    # use the provided key as sender and signer
    params.merge!({
      from: sender_key.address,
      nonce: get_nonce(sender_key.address),
    })
    tx = Eth::Tx.new(params)
    tx.sign sender_key
    return eth_send_raw_transaction(tx.hex)["result"]
  else
    # use the default account as sender and external signer
    params.merge!({
      from: default_account,
      nonce: get_nonce(default_account),
    })
    return eth_send_transaction(params)["result"]
  end
end