That only works for apps that are exclusive to Apple devices or that have separate licenses for Apple devices. If I buy Epic in-game currency from Epic and use

That only works for apps that are exclusive to Apple devices or that have separate licenses for Apple devices. If I buy Epic in-game currency from Epic and use it on my PC to buy some skin, and then use the skin I bought that way when playing on my iPhone, should Apple get a cut of the money? If yes, how much? The cost of the skin, or the cost of the in-game currency (maybe I bought a 10 USD bundle, but the skin only cost 1 USD, the other 9 USD is just staying in my account unused)?