C#: Resource for parameter [extensionId] is not found

I am trying to pull users presence data in C#

I was able to get the AccountId and the ExtensionId from here:

Here is my code:

using System;
using System.Threading.Tasks;
using RingCentral;

namespace Send_SMS
{
    class Program
    {
        const string RINGCENTRAL_CLIENTID = "<>";
        const string RINGCENTRAL_CLIENTSECRET = "<>";

        const string RINGCENTRAL_USERNAME = "<>";
        const string RINGCENTRAL_PASSWORD = "<>";
        const string RINGCENTRAL_EXTENSION = "<>";

        const string RINGCENTRAL_PRESENCE_USER = "<>";
        const string RINGCENTRAL_PRESENCE_EXT = "101";


        static RestClient restClient;

        static void Main(string[] args)
        {

            restClient = new RestClient(RINGCENTRAL_CLIENTID, RINGCENTRAL_CLIENTSECRET, false);
            restClient.Authorize(RINGCENTRAL_USERNAME, RINGCENTRAL_EXTENSION, RINGCENTRAL_PASSWORD).Wait();
            get_presence().Wait();

        }
 
        static private async Task get_presence()
        {

            // OPTIONAL QUERY PARAMETERS
            ReadUserPresenceStatusParameters readUserPresenceStatusParameters = new ReadUserPresenceStatusParameters
            {
                //detailedTelephonyState = true,
                //sipData = true
            };

            var response = await restClient.Restapi().Account(RINGCENTRAL_PRESENCE_USER).Extension(RINGCENTRAL_PRESENCE_EXT).Presence().Get(readUserPresenceStatusParameters);

            Console.WriteLine("Presence for Test Account: " + response.presenceStatus);
        }

    }
}

Everything in <> is filled out of course, and tested with the SMS_Send tutorial.

My error:

Content: {"errorCode":"CMN-102","message":"Resource for parameter [extensionId] is not found","errors":[{"errorCode":"CMN-102","message":"Resource for parameter [extensionId] is not found","parameterName":"extensionId"}],"parameterName":"extensionId"}

Thanks in advance. I'm really struggling to understand the account/extension side of this API.