Refactor C# SMS Routine for Africastalking

I have a desktop application that was originally compiled in C#. Its only task that now needs attention is the SMS routine. At the moment the program calls a small, home-grown web service; I can share full documentation for that existing endpoint so you will immediately see the parameters and payload it expects. Here is the new goal: whenever the application sends a message it must instead post to Africastalking’s bulk messaging REST endpoint ( https://api.sandbox.africastalking.com/version1/messaging/bulk ). All other behaviour in the app should remain untouched. I already own commercial decompilation tools and can provide you with a clean project skeleton produced from the executable, so you can focus purely on refactoring the SendSms() logic, wiring in the required headers, URL parameters, JSON body and authentication for Africastalking. Deliverables • Updated source files (or a self-contained class / DLL) that replace the current SMS method • A rebuilt executable demonstrating successful delivery through the Africastalking sandbox, with the request/response captured for verification • Brief notes on the code changes so I can maintain the project in future Acceptance criteria The rebuilt app must compile without warnings in Visual Studio, send messages that appear in my Africastalking dashboard, and display any API error returned by Africastalking exactly once to the user. If you have recent experience integrating Africastalking or similar REST gateways in C#, this will be a quick, focused task. Feel free to suggest the cleanest way to structure the new call—HttpClient, RestSharp, or another lightweight approach—as long as it keeps external dependencies to a minimum.