In this code, I get the error for rcsdk.token.access_token.Length and rcsdk.Restapi().Account().Extension().PhoneNumber().Get(); like "The name 'rcsdk' doesn't exist in the current context"

static private async Task read_extension_phone_number()

        {

            if (rcsdk.token.access_token.Length > 0)

            {

                var resp = await rcsdk.Restapi().Account().Extension().PhoneNumber().Get();

                foreach (var record in resp.records)

                {

                    if (record.usageType == "DirectNumber")

                    {

                        foreach (var feature in record.features)

                        {

                            if (feature == "SmsSender")

                            {

                                send_sms(record.phoneNumber).Wait();

                                goto LoopEnd;

                            }

                        }

                    }

                }

            }

How can I fix it?

And also why this var string try to be a bool?

const string RINGCENTRAL_PRODUCTION = false;

Code from here https://developers.ringcentral.com/guide/messaging/quick-start#c#