Could not sign Transaction with SignRawTransactionWithKey through the RPC (RegTest)

Question

I am able to sign following transaction with Complete=true result, but when trying to decode signed transaction, it returns error "TX decode failed" both from DecodeRawTransaction and SendRawTransaction RPC calls.

signed_Tx = "020000000103d3049e968d8b3e3e967aa90b45d3f64b5e2117ee9610b0c9d5a96081a24e3e000000004847304402201921a1acf601acb0f9e6297a55eeb853c2dd6cd246ea05f060eaa4d327d4124a02206e08e2c90b92113a64d6de1447f81bf19703f88bffeacc6d2cc4bf0e21ed8ac501ffffffff0200e1f5050000000017a9140796253e13d88cda530bf88b07eb1672952a3a7887608a0e24010000001976a914957b73da3bf34440ab2f78937a7a420835255a0988ac00000000"

[TestMethod()]
public async Task CreateRawTxTest()
{
    Dictionary<string, object> prevTx = new Dictionary<string, object>() {
                    { "txid","3e4ea28160a9d5c9b01096ee17215e4bf6d3450ba97a963e3e8b8d969e04d303"} ,
                    { "scriptPubKey", "21033ff1181726af279fb2328e9ae041d71f323a91483f76841fe23aa03f87ecf3d3ac" },
                    { "vout", 0} };

    List<object> txIn = new List<object>()
            {
                new Dictionary<string, object>() {
                    { "txid","3e4ea28160a9d5c9b01096ee17215e4bf6d3450ba97a963e3e8b8d969e04d303"},
                    { "vout", 0} }
            };

    List<object> txOut = new List<object>()
            {
                new Dictionary<string, float>
                {
                    { TestNet_ReceiverAddress, 1.0f}
                },
                new Dictionary<string, float>
                {
                    { "TestNet_SenderAddress", 48.99900f }
                },
            };


    RPCResultPrime<string> rawResult = await disp.CreateRawTransactionAsync(txIn, txOut);

    if (rawResult.Error == null)
    {
        string TxRaw = rawResult.Result;

        Dictionary<string, object> param = new Dictionary<string, object>()
                {
                    {"hexstring", TxRaw },
                    {"privkeys", new string[] { PrivateKey }},
                    {"prevtxs", new List<object>(){ prevTx } }
                    {"sighashtype", "ALL" }
                };

        string signedTx = await disp.SignTransactionAsync(param);

        //at this point transaction signed successfully but could not be Decoded in the next step

        string decode = await disp.DecodeRawTransactionAsync(signedTx);

        string jsonSend = await disp.SendRawTransactionAsync(signedTx);

        Debugger.Break();
    }

}

Answer 1

Seems to be able to be decoded:

$ bitcoin-cli -regtest decoderawtransaction 020000000103d3049e968d8b3e3e967aa90b45d3f64b5e2117ee9610b0c9d5a96081a24e3e000000004847304402201921a1acf601acb0f9e6297a55eeb853c2dd6cd246ea05f060eaa4d327d4124a02206e08e2c90b92113a64d6de1447f81bf19703f88bffeacc6d2cc4bf0e21ed8ac501ffffffff0200e1f5050000000017a9140796253e13d88cda530bf88b07eb1672952a3a7887608a0e24010000001976a914957b73da3bf34440ab2f78937a7a420835255a0988ac00000000
{
  "txid": "9cbedd5f9674aff9fff890cec60aa38dba074fcc3984c5a2b760ff69d2c9ea3f",
  "hash": "9cbedd5f9674aff9fff890cec60aa38dba074fcc3984c5a2b760ff69d2c9ea3f",
  "version": 2,
  "size": 189,
  "vsize": 189,
  "weight": 756,
  "locktime": 0,
  "vin": [
    {
      "txid": "3e4ea28160a9d5c9b01096ee17215e4bf6d3450ba97a963e3e8b8d969e04d303",
      "vout": 0,
      "scriptSig": {
        "asm": "304402201921a1acf601acb0f9e6297a55eeb853c2dd6cd246ea05f060eaa4d327d4124a02206e08e2c90b92113a64d6de1447f81bf19703f88bffeacc6d2cc4bf0e21ed8ac5[ALL]",
        "hex": "47304402201921a1acf601acb0f9e6297a55eeb853c2dd6cd246ea05f060eaa4d327d4124a02206e08e2c90b92113a64d6de1447f81bf19703f88bffeacc6d2cc4bf0e21ed8ac501"
      },
      "sequence": 4294967295
    }
  ],
  "vout": [
    {
      "value": 1.00000000,
      "n": 0,
      "scriptPubKey": {
        "asm": "OP_HASH160 0796253e13d88cda530bf88b07eb1672952a3a78 OP_EQUAL",
        "hex": "a9140796253e13d88cda530bf88b07eb1672952a3a7887",
        "reqSigs": 1,
        "type": "scripthash",
        "addresses": [
          "2MswLavAixrNJY2eN58LLT6xjwLqouwvASn"
        ]
      }
    },
    {
      "value": 48.99900000,
      "n": 1,
      "scriptPubKey": {
        "asm": "OP_DUP OP_HASH160 957b73da3bf34440ab2f78937a7a420835255a09 OP_EQUALVERIFY OP_CHECKSIG",
        "hex": "76a914957b73da3bf34440ab2f78937a7a420835255a0988ac",
        "reqSigs": 1,
        "type": "pubkeyhash",
        "addresses": [
          "mu9LsGdG3KFnpgB3Vx8w1sg8uCLb4gn3Uk"
        ]
      }
    }
  ]
}

Answer 2

You are passing the parameter with signedTx incorrectly. A JSON-RPC param key must have a value that is either an array or an object. You are passing in a string. Instead you should pass in the parameter similarly to how you did for the signrawtransactionwithkey call.

You should have something like this:

     Dictionary<string, object> param = new Dictionary<string, object>()
            {
                {"hexstring", signedTx }
            };

    string decode = await disp.DecodeRawTransactionAsync(param);

The same should be done for sendrawtransaction.