Send #Whatsapp message with WhatsApp #API
The WhatsApp Business API is open for applications, which you can sign up for via https://www.facebook.com/business/m/whatsapp/business-api – and it looks like they are working with Twilio to create a webhook layer on top of this.
But, there are some simple things you can do today, for example, if you want to encourage your users to send you a WhatsApp message from your app or website, then you can add a link to;
https://api.whatsapp.com/send?phone=<your number>&text=hello
It’s important to remember that whatsapp is not typically used from the desktop, so if you want this to work, and your user is on a desktop browser, then it is better to show a QR code for the URL above – that they can scan with their phone, rather than sending them directly to this url.
Once this API is in general release, it’ll be a new feature that we’ll add to https://www.cloudansweringmachine.com
Network Programming in .NET 
You can use REST API https://api-messenger.com/
Message sending limits are very large. Free demo access for 3 days
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