What is subscribers?
Subscribers are customers who have inboxed fanpage and you can send them free messages at any time.
You can manage the subscribers at Customer. A subscriber is a customer with the “sub” status. If they don’t want to receive advertisements, they can send “stop”, Fchat will change their status into “Unsub.”
Fchat's service packages are based on the number of subscribers stored on fchat and having the “sub” status. You can delete customers who have not inboxed / read the message for a long time (last seen > 6 months) to avoid paying additional service fees.
Facebook's 24 hours policy: Fanpage will have up to 24 hours to respond to a user. Messages sent within the 24-hour period may contain promotional content. After 24 hours, you must not send messages containing promotional content. If this is violated, the page may be blocked from sending message features.