WhatsApp message templates can be sent proactively. This means you can send them to contacts who have never sent you a WhatsApp message in the past.
However, you must obtain and keep a record of your user's consent before sending them a WhatsApp message for the first time.
For more information on this, https://developers.facebook.com/docs/whatsapp/guides/opt-in/
Please note the following paragraph from the official guide:
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People can block or report businesses, and our systems will rate limit businesses if the business’ quality is low for a sustained period of time. We may also reactively evaluate a business’ opt-in flows, including user feedback, to flag policy violations and develop additional types of enforcement over time. |