A user must first consent to receive messages in WhatsApp by opting into them via a third-party channel. This can be any channel your business uses to communicate with people today — your website, app, email, SMS, retail location, etc.
The opt-in must be an active opt-in. This means it must be triggered by a user action, such as entering a phone number or checking a box to indicate consent.
Clear opt-in messaging so that a user knows what type(s) of messaging the person is signing up for.
Required language elements:
“receive [noun], [logo and name], on [number]"
Where noun is type of information related to the flow.
User must be asked to opt-in via a visual element (checkbox or similar) shown next to the WhatsApp name and logo on your chosen third party channel. The user should have control over what number is used through explicit action (e.g., editing). In addition, language must be shown adjacent to the UI elements to explain clearly what information will be received and make specific reference to this information being sent as messages on WhatsApp.