144h visa-free requirements

Hi
I plan to fly to south korea with a transit in Beijing where I will stay 6 days.
To apply for the 144h visa-free it is required to show to the custom office my fly tickets with the seat number from Beijing to Seoul. Unfortunatly I have only a document with my e-ticket number, without seat number. Is it OK for the custom office If I show only my e-ticket document without seat number ? Thank you.