ASP.NET WhatsApp API Integration

I need to plug full WhatsApp functionality into my existing ASP.NET C# web application. The goal is a clean API layer that can both send and receive messages in real time. Outgoing traffic must handle plain text as well as images, video, or other multimedia, and the code should address delivery to individual contacts and group chats alike. Incoming traffic should arrive in a structured model I can consume server-side, with webhook handling (or equivalent) for status updates and replies.

Please build the integration with clear, well-commented C# code and an easy-to-adapt configuration file (keys, tokens, webhook URLs, etc.). I’m open to the official WhatsApp Business Cloud API, Twilio, or another reliable provider—whichever you feel offers the best balance of stability and cost.

Deliverables
• Visual Studio solution (ASP.NET c# or Web API) containing the integration layer
• Sample controller/endpoints that show:
 – sending text
 – sending multimedia (image & video examples)
 – receiving and parsing incoming messages
• README explaining setup, environment variables, and how to switch between sandbox and production numbers
• Quick test script or Postman collection to demonstrate every endpoint

Acceptance criteria
• Messages successfully reach both a single contact and a group in my test account
• Incoming messages fire the webhook and populate the provided model without loss of metadata (sender, media URL, timestamp)
• All external dependencies documented and included via NuGet where possible
• Code compiles under the latest LTS version of .NET and runs locally with minimal setup