When trying to book a transit hotel with Air China, the message "The ticket is not eligible for this service, or the product stock for the service date you have selected is exhausted." appears. By all criteria, the ticket meets the conditions for providing a transit hotel, so I conclude that there are no more available rooms. Is it worth spending time and trying to book a hotel with Air China during the layover in Beijing, or will there definitely be no available rooms and it's better to book a hotel?
Try calling them, we have representations of some airlines in Russia.
Or approach the airline representatives at the airport. There are plenty of hotels in Beijing, worst case scenario, you can reserve on the spot. There is Wi-Fi at the airport.