Welcome to the RingCentral Community

We do have a C# SDK available, and there are examples for SMS, Fax, and other services offered by the RingCentral API resources. RingOut is a two-legged call. The SDK contains all the information you'll need to get started using it in your application.

The RingCentral C# SDK: https://github.com/ringcentral/ringcentral-csharp

Example request to establish a two-legged ringout:

Request request = new Request("/restapi/v1.0/account/~/extension/~/ringout", jsonRingoutString);
Response response = ringCentral.Post(request);

The API Documentation for Two-Legged RingOut which provides information you'll need when populating the JSON body of the POST request: https://developer.ringcentral.com/api-docs/latest/index.html#!#TwoLegRingOut.html