Confused if I’m approved for free transit

Also, I’m entering through Honk Kong to Beijing... since my roundtrip ticket is from US to Hong Kong. Then have a separate flight from Hong Kong to Beijing and another flight from Beijing to Hanoi. I will be in Beijing for 48hrs and have a flight booked from Beijing to Hanoi Vietnam. Is this approved and all the documents I need to provide? Sorry this is all a bit confusing.