Invoking the listunspent command via json-rpc on a full node
The issue is that you are sending the 1000 parameter as a string, not as a number. The JSON type when the RPC server receives it will be a string, which is incorrect. It does not convert this to an integer implicitly so you need to explicitly set the type. So instead you should be doing:

JObject data = JObject.Parse(RequestServer("listunspent", new List&lt;Integer&gt;() { 1000 }));