im flying from Hanoi to Macau cross into zhuhai chimelong then fly back to HoChiMinh(saigon)

You can do the following:

- scenario 1: You can do this, but just by applying and obtaining a Zhuhai 3 days visa on arrival at the border crossing between Macau and mainland China. This is fine and easily doable, but the main drawback is the steep price of 1,295 CNY of visa for US citizens due to reciprocity. By the way, we both know that there are no direct flights between Macau and Ho Chi Minh, but you can really fly from Macau wherever you want. Please, have in mind that you cannot use Zhuhai airport under Zhuhai VOA because Zhuhai airport is domestic only airport.

- scenario 2: This is perfectly doable and if there are no additional landings within mainland China beside Beijing, you are definitely eligible for 144 hour visa free transit in wider Beijing area and no visa is needed. Also, this option does not imply any fee.