Thanks for your help guys!
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I think this is not an automatic solution, WhatsApp is not open for everyone, you must make a register and be approved to send messages to your users, and your users must opt-in first. You can't send some things like promotions yet.
you can use mixpanel as the target selecting criteria (events, users etc) to send your messages from twilio, and twilio has a whatsapp integration https://www.twilio.com/whatsapp
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