Quick Answer
Cocoa powder does not use the same grams-to-cups value as every other ingredient. Using a practical US cup reference, 99 grams of cocoa powder is about 1 cup.
That means 100 grams of cocoa powder is about 1.01 cups, while 200 grams is about 2.01 cups.
Cocoa powder is fluffy and can clump, so how it is scooped or sifted affects the cup value.