Method not found: 'Void RestSharp.RestRequest..ctor(RestSharp.Method)

Questions API
1

am calling the UserApi but am getting the Method not found: 'Void RestSharp.RestRequest…ctor(RestSharp.Method)

lib used Okta.SDK .net v 6.0.9
RestSharp Version=110.2.0
JsonSubTypes Version="2.0.1

            Configuration config = new Configuration();
            config.OktaDomain = "https://XXXX-XXXXX.oktapreview.com";
            // Configure API key authorization: apiToken
            config.Token = "XXXXXXXXXXXX";

            var userApi = new UserApi(config);

            return await userApi.CreateUserAsync(userRequest, activate, provider, nextLogin);

can you guys let me know what is missing here.