I'm looking for a way to send WhatsApp messages to users on behalf of users. I'm developing a web app that uses TalkJS as our chat platform and we want to offer users a seamless chat experience across different channels. For instance, let's say Alice and Bob are chatting on our web app. We want Alice to be able to send a message to Bob through our web app, and have that message also delivered on WhatsApp to Bob's phone number. And if Bob replies on WhatsApp, we want Alice to receive that reply on our web app. I don't think this is possible because WhatsApp doesn't allow third-party apps to send messages on behalf of users, but I wanted to ask if anyone has encountered this problem before and found a workaround or a solution for it.
To answer my question, it's not possible to achieve the feature described above. WhatsApp doesn't allow third-party applications to send messages on behalf of users using their personal phone numbers. This restriction applies universally, including to other applications like ClickSend. Messages can only be sent from owned numbers and not from an individual user's number.