When you initiate a request via Messenger, the business has 24 hours to respond. However, replying back via an "eligible action" (like typing "learn more" or "make appointment"), resets the clock. Those who subscribe to a company's Messenger feed, by comparison, will get messages unprompted and more regularly, but no promotional content is allowed. If subscribers reply to a message, however, it will switch into standard messaging mode, meaning ads and promos are fair game.
Existing companies using the service have three months to comply to the new rules for standard messaging, which are now in effect. For firms who want to start, Facebook promises to review new bots within five days.
The new subscription options are starting in beta for companies involved in news, productivity and personal trackers (bots used for fitness, health wellness and finance). Any interested organizations have six months to tell Facebook how, exactly, they plan to use it -- presumably, Facebook doesn't want the experience to be too spammy.
The service is a crafty way for Facebook to monetize its 1 billion monthly Messenger users, since it keeps folks in control of promotions. There are reportedly 18,000 bots on the service, and 23,000 companies using Facebook's own "Wit.ai" deep learning tech that enables natural language recognition.