What is Opt-in?
Opt-in is a person’s consent to receive communications. On social media, Meta requires that an account only send messages outside the 24-hour window to people who explicitly said yes, in a step where the person understands what they will receive. Opt-in protects the account from being flagged as spam and is what separates a contact list from a sending list. The person can leave at any time, and the account has to respect that.