In cases when the channel shows that the Room status is closed (in red), and especially if this option was set manually on the Booking Extranet before, it is necessary to adjust this before connecting to channel manager. You can check this on Your Extranet calendar.
Rentlio channel manager controls your Rooms to sell only, but your Room status can not be controlled by Rentlio.
On Your Booking Extranet under Open/close rooms option it is necessary to open all rooms for a certain date or period, (preferably until the time when availability is added in Rentlio) by selecting Rates & Availability:
After this, Your rooms status would be bookable (in green):