It's unclear if the merchants of Yap already had an online shop. But at some point they realized what most societies realize. They needed something that everyone agrees you can use to sell your stuff online.
Each rock’s worth is based on its size and its history (where it came from). Though US dollars have now started to be used for everyday purchases on the island, rocks are still used for ceremonial transactions (during weddings, for example). Yap also uses turmeric, shells and cloth as official currency.amazing-facts-about-travel