This is a question we have from time to time. We monitor the domain using the Widget to prevent Abuse or Spam. Also we want to avoid the use of a Widget in multiple domains. To control the use, we need to link a domain to the script we give you.
So, if you are working a pre-production environment or your website is not life, you can not test the solution.
We know this is an issue, but we need a real domain to test the Widget.
You can use something like www.mydomain.com/client-website and create a Widget for “mydomain.com”. That way you will be able to test the solution.
The WhatsApp Widget can not work in a local development (your local machine). You need to have the development (Drupal, PHP, Joomla) in a server online with an active domain.