A question about the ticket w/confirmed seat

I'd like to fly from Hong Kong to Helsinki, Finland via Beijing and would like to use the 144-hour free transit.
However, the requirements say that "Passengers should hold an onward ticket with a confirmed seat". Unfortunately, I cannot get a real ticket w/confirmed seat number before I check-in. My airline, Finnair, allows to check in online no earlier than 36 hours before the flight. Is it allowed to present the paid booking confirmation?
Thank you.