There are open and close channels. Information posted on an open channel is available for any user of the messenger. A close channel is different, its content is hidden from users who do not follow it. The owner can invite users to their channel or generate a link following which a user also can join the channel. The content posted on a close channel is available to you only after joining it. Some advertisers close their channels, when publishing promo posts, to lower the price for followers and learn how many of them will buy.