Onward ticket and Vietnam 'Visa approval letter' qualify for 72h free transit?

I'm flying from Amsterdam to Beijing and 2 days later onwards from Beijing to Hanoi. Vietnam has a requirement. but it can be picked up on arrival in Hanoi with a 'Visa approval letter', so I won't have the actual Vietnam visa yet while in China. Will the onward ticket and the 'approval letter' qualify for the 72h free transit?