We are programming a marketplace for digital artwork, which shall use in-app purchases. Are we allowed/supposed to create only one storekit product, which we can call "item-x" and assign a fix price of i. e. 5,00$, assuming all items are sold for 5,00$, and use this product for all items? Or shall we create one product for each item which is selled on or platform, which could be 1.000?