(.net core) how eth_sendRawTransaction

help,I used the following code to get this error
— ```
Nethereum.JsonRpc.Client.RpcResponseException: transaction could not be decoded: could not decode RLP components: extra data at end: eth_sendRawTransaction

(I authorize fromAddress to adminAddress , initiate transfer through adminAddress , and transfer to toAddress)

var adminKey = con.GetSection(“Admin:Key”).Value;
var adminAddress = con.GetSection(“Admin:Address”).Value;
var account = new ManagedAccount(adminAddress,adminKey );
var url = “https://mainnet.infura.io/v3/xxxx
var web3 = new Web3(account, url );
Contract contract = web3.Eth.GetContract(usdtAbi,usdtAddress);
TransactionInput txinput = new TransactionInput();
txinput.From = fromAddress;
txinput.To = toAddress;
txinput.Value = new HexBigInteger(1000000);
txinput.Nonce = 26;
EthereumMessageSigner signer1 = new EthereumMessageSigner();
var signature1 = signer1.EncodeUTF8AndSign(txinput.ToJson(), new EthECKey(adminKey));
var rrr = await web3.Eth.Transactions.SendRawTransaction.SendRequestAsync(signature1);

Hey, are you still having the problem ?