What WhatsApp allows outside a conversation, and what that means for you.
WhatsApp does not let a business message someone out of the blue in free text. Outside a 24-hour window that opens when the client messages you, only a message template approved by Meta can be delivered.
A reminder the day before an appointment is exactly that kind of message, so it goes out as a template. We maintain the template, submit it, and keep it approved - there is nothing for you to set up.
What you do need is WhatsApp on your plan. Without it the reminder cannot be delivered, and WhatsApp is not offered as a channel when adding a rule.
Did this leave something out? Email support@kuai.io.