I'm able to deploy my contract to sepolia. I have ABI, Bytecode of deployed contract.

in .NET environment in register method I have:

                    var senderAddress = "0xF428E821e8D5f89031F38a0E5eA3419735c150a7"; 
                    var contractAddress = "0x*";
                    var web3 = new Web3("https://sepolia.infura.io/v3/*");
                    var carContract = new CarRegistrationContract(senderAddress, contractAddress, web3);
                    var transactionHash = await carContract.AddCarAsync("ABC123", 50000, 123, 456);
                    Console.WriteLine("Transaction Hash: " + transactionHash);
                    return true;
                catch (Exception ex)

and my AddCarAsync method looks like this

public async Task<string> AddCarAsync(string vin, BigInteger milage, BigInteger eventCode, BigInteger dealershipId)
            var addCarFunction = contract.GetFunction("addCar");
            var gasPrice = Web3.Convert.ToWei(20, UnitConversion.EthUnit.Gwei);
            var gasLimit = 21000;

            var encodedData = addCarFunction.GetData(vin, milage, eventCode, dealershipId);
            var transactionInput = new TransactionInput()
                Data = encodedData,
                GasPrice = new HexBigInteger(gasPrice),
                Gas = new HexBigInteger(gasLimit),
                To = contractAddress

            //The method eth_sendTransaction does not exist/is not available: eth_sendTransaction
            var transactionHash = await web3.Eth.Transactions.SendTransaction.SendRequestAsync(transactionInput);
            return transactionHash;

I catch an error, in 'SendRequestAsync': The method eth_sendTransaction does not exist/is not available: eth_sendTransaction

Not sure what is going on, and what to do with this? Should I sign this transaction somehow? I tried but with no luck. Need some guidance from more experienced devs. Thanks

2 Answers 2


eth_sendTransaction is a method that assumes you have access to a node that you fully manage yourself and the node manages your private key and signs the transaction. eth_sendTransaction is not supported by node providers for security reasons.

What you want to use instead is eth_sendRawTransaction, in which you construct & sign the transaction locally and then send it to the remote node to propagate.

  • Thanks, that was the issue
    – michal
    Oct 27, 2023 at 10:55

This is a solution for my issue

var account = new Account(_walletPrivateKey);var nonce = await _web3.Eth.Transactions.GetTransactionCount.SendRequestAsync(account.Address, BlockParameter.CreatePending());var gasPrice = Web3.Convert.ToWei(10, UnitConversion.EthUnit.Gwei);var gasLimit = 1000000;

var functionInput = new AddCarFunction
  Vin = vin,
  Milage = (uint)milage,
  EventCode = (uint)eventCode,
  DealershipId = (uint)dealershipId,
  Nonce = nonce,
  Gas = new HexBigInteger(gasLimit),
  GasPrice = new HexBigInteger(gasPrice),
var transactionInput = functionInput.CreateTransactionInput(_contractAddress);

var offlineTransactionSigner = new AccountOfflineTransactionSigner();
var txtSigned = offlineTransactionSigner.SignTransaction(account, transactionInput);
var txtHash = await _web3.Eth.Transactions.SendRawTransaction.SendRequestAsync(txtSigned.EnsureHexPrefix());

return txtHash;

now I'm able to interact with my contract on testnet.

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