Answer
There's no native WhatsApp integration in IFS. What IFS does support natively is SMS — on Apps10 and later, this is done via IFS Connect's HTTP Sender, calling out to a third-party SMS/messaging gateway's own API (the older dedicated SMS_SENDER connector functionality was removed from IFS Connect starting around Apps9 and isn't available in current releases). The same general pattern — an event or scheduled job building a message and posting it to a third-party messaging gateway's REST API via HTTP Sender — is the realistic route for something like a WhatsApp Business API integration too, though that would be a custom integration built the same way an SMS gateway integration is, not an out-of-the-box IFS capability.