If you want to reach out to and initiate a conversation with your customers with outbound messaging via the WhatsApp Business solution, you need permission (opt-in) from that customer. This active opt-in can be obtained via any channel you already use to communicate with your customer, for example your company website, app, email, SMS, store and even WhatsApp itself. You also need to comply with applicable law, like GDPR.
Active opt-in for receiving WhatsApp messages
The opt-in must be an active one. This means the opt-in is done by a user action, for example when the customer enters his phone number or checks a box to give consent to you using his number for WhatsApp messaging. Also, you need to clearly inform the customer on what exactly he is opting in for. So, what type of messages will the customer receive? This doesn’t mean ‘WhatsApp message’, but what type of content you will be sharing, for instance: "For the purpose of sending you your purchase receipt"
A good example of opt-in design would be a visual element (check box or similar) next to the WhatsApp name + logo. The user can enter or edit the phone number, meaning he has control over what number is used. Also, it is explained clearly what information will be received and that this will be shared via WhatsApp.
A customer sending a message to a company is therefore strictly not an opt-in. If a customer sends you a message, you may send him replies for the duration of the customer care window. If you want to send notifications, an opt-in is required.
Once you have obtained the opt-in, you can send the consumer one of the templates you have had approved by WhatsApp.