.call.start()

This API enables initiating a call when an external button on the site is clicked. This method can be invoked only from inside a JavaScript OnClick event handler.

Note: 

• If the name, email, and phone fields are marked as mandatory in your brand settings (Settings > Brands > Select your brand > Flow Controls > Online/Offline fields), ensure to set these required fields using visitor.name(), visitor.email(), and visitor.contactnumber() API. 
• Additionally, the .chat.department() API can be used to display the departments before the call is initiated.