Do customers need to opt-in to receive WhatsApp messages from my business?
Yes. Your customers must consent to receive messages in the WhatsApp Business API. This can be done by opting via a third channel — such as your website, app, email, SMS, retail location, etc. Also, the user must actively opt-in — by entering a phone number, checking a box in a form, or another action to indicate consent. You can find more information on how to setup opt-ins here.
Once the user is opted-in, you can initiate a conversation with your customer with a pre-approved message template.