Only replay-protected (EIP-155) transactions allowed over RPC

import { Wallet, JsonRpcProvider, parseEther, parseUnits } from "ethers";

const provider = new JsonRpcProvider("https://ethereum-mainnet.core.chainstack.com/AUTH_KEY");
const wallet = new Wallet(process.env.PRIVATE_KEY!, provider);

// ethers picks up chainId automatically from the provider.
// For manual construction, include it explicitly:
const tx = await wallet.sendTransaction({
  to: "0xRecipientAddress",
  value: parseEther("0.1"),
  gasLimit: 21000,
  maxFeePerGas: parseUnits("50", "gwei"),
  maxPriorityFeePerGas: parseUnits("2", "gwei"),
  chainId: 1, // Ethereum mainnet
});

import { createWalletClient, http, parseEther, parseGwei } from "viem";
import { mainnet } from "viem/chains";
import { privateKeyToAccount } from "viem/accounts";

const account = privateKeyToAccount(process.env.PRIVATE_KEY as `0x${string}`);
const client = createWalletClient({
  account,
  chain: mainnet, // chain object carries the chain ID
  transport: http("https://ethereum-mainnet.core.chainstack.com/AUTH_KEY"),
});

const hash = await client.sendTransaction({
  to: "0xRecipientAddress",
  value: parseEther("0.1"),
  maxFeePerGas: parseGwei("50"),
  maxPriorityFeePerGas: parseGwei("2"),
});

from web3 import Web3

w3 = Web3(Web3.HTTPProvider("https://ethereum-mainnet.core.chainstack.com/AUTH_KEY"))
account = w3.eth.account.from_key(PRIVATE_KEY)

tx = {
    "to": "0xRecipientAddress",
    "value": w3.to_wei(0.1, "ether"),
    "gas": 21000,
    "maxFeePerGas":         w3.to_wei(50, "gwei"),
    "maxPriorityFeePerGas": w3.to_wei(2,  "gwei"),
    "nonce":   w3.eth.get_transaction_count(account.address, "latest"),
    "chainId": w3.eth.chain_id,  # fetched once and reused
}
signed = account.sign_transaction(tx)
tx_hash = w3.eth.send_raw_transaction(signed.raw_transaction)