WhatsUp Business integration is restricted compared to the free 1:1 chat know commonly to us.
For example, if you attempt to send the first message to a contact, you have to pay a fee + to greet the customer via a pre-approved template from Facebook. After 24h the coms channel closes. Also, each company would require to complete a vetting process to use the API integration which 3CX would need to bring you the messages into your WebClient. FB/WA intent this only for Enterprise business, SME will only be served via the WA Business app.
Therefore there is little for us to offer you, LiveChat has a much higher functionality currently.
For the time being, I will label it rejected until the WA landscape in this matter changes. We are monitoring it closely!