Hello, WhatsApp's official API is named 'WhatsApp Business.' It isn't free and has certain limits. There are some third-party solutions, unofficial APIs, that can work around those limitations, but they are also expensive to use. If you are interested, I have created an unofficial API for a customer here on Freelancer. It was a long time ago, so the same solution probably needs some changes or maybe even a full rework, but I certainly have full knowledge of how to make this API work because I have spent many hours learning all things that are involved when making a project like this. The API was basically an invisible web browser that was running in the background and can be used just like a normal API DLL library in C#. It can send and receive messages, images, etc. The entire API was oriented around the WhatsApp web version of the app. If you are interested in more details, please feel free to send me a direct message.