I have a 2 hr layover in China. I hold a St Lucian passport. How do i apply for the 24 hr visa.

Actually, you do not need any kind of visa. Your transit through China will be covered by 24 hour visa free transit. It is important to know that this is not a transit visa, but you travel covered by 24 hour visa free transit, so there is no any kind of visa.

You will just declare at your starting point at check in in the country from where you will depart toward China, that you will travel to country X by making a short transit in China by relying on 24 hour visa free transit. After that, you will be allowed to proceed to the plane.

Upon your arrival in China, if you transit through some larger airport, you will not even be a subject of immigration and customs control, but you will just cross security check and proceed to your gate for your onward flight from China to your final destination. Your passport is all you need. Have a nice journey.