Vietnamese Passport holder eligibility

I'd like to confirm my eligibility status: Vietnamese Passport holder, German visa, no China visa, traveling from Hanoi (Vietnam) - Shenzen - Beijing - Munich (Germany). I will be on one China domestic flight (Shenzen - Beijing). I will arrive Shenzen and leave Beijing on the same day, within 24 hours of arrival. Does this mean I only need to fill out some forms in the airport border counter at Shenzen for a 24h temporary entry permit? What documents should I bring to get that temporary entry permit? Thank you for your answer.