Trouble posting CREATERAWTRANSACTION to Bitcoin Core via JSON-RPC

I think the problem is your params array is getting double-serialized, so the server doesn't know how to interpret the request. I do realize that your JSON looks the same as the example, so I could very well be wrong here; I'm definitely not an expert on using Bitcoin Core's API. However, I did look at a the source code for a third-party library which is supposed to be compatible with Bitcoin Core, and it does not appear to double-serialize the parameters for the createrawtransation request. This leads me to believe that the double-serialized parameters are the problem.

To fix, try the following:

1. Change the method signature for your existing RequestServer method from this:

   public static string RequestServer(string methodName, List<string> parameters)

   to this:

   public static string RequestServer(string methodName, List<JToken> parameters)

2. Create a new overload of the RequestServer method using the old signature which calls the existing one you just changed. This will allow your other methods which already work (e.g. sendtoaddress and listunspent) to keep working with no changes.

   public static string RequestServer(string methodName, List<string> parameters){    return RequestServer(methodName, parameters.Select(p => new JValue(p)).ToList<JToken>());}

3. Lastly, change the code in your button1_Click method so that it does not serialize jArray and jArray2, but instead passes them in a List<JToken> to RequestServer. In other words, change this code:

   string strFrom = JsonConvert.SerializeObject(jArray);string strTo = JsonConvert.SerializeObject(jArray2);data = JObject.Parse(RequestServer("createrawtransaction", new List<string>() { strFrom, strTo }));

   to this:

   data = JObject.Parse(RequestServer("createrawtransaction", new List<JToken>() { jArray, jArray2 }));

With these changes, the RPC JSON for createrawtransaction should end up looking like this:

{"jsonrpc":"1.0","id":"1","method":"createrawtransaction","params":[[{"txid":"1a43a1f27c5837d5319a45217aa948a4d39c1d89faf497ce59de5bd570a64a26","vout":1}],[{"2NAZpRsvj9BstxxCDkKoe1FVjmPPxdmvqKj":0.01}]]}

Notice that the extra quotes and backslashes in the params array are gone. Compare to what you had before:

{"jsonrpc":"1.0","id":"1","method":"createrawtransaction","params":["[{\"txid\":\"1a43a1f27c5837d5319a45217aa948a4d39c1d89faf497ce59de5bd570a64a26\",\"vout\":1}]","[{\"2NAZpRsvj9BstxxCDkKoe1FVjmPPxdmvqKj\":0.01}]"]}