How a phone number gets on the list
Recipients do not sign up themselves. While setting the app up on the parent’s phone, a family member asks each relative for permission and enters a name and number only after they agree. The app reminds them to ask and offers the words to use (the consent script).
Each number then receives one message saying which parent it is about and what they will receive, with a link to stop. The link keeps working for as long as the number is on the list.