At this time, United States dollars (USD) are the only supported currency for the Sell Block.
International buyers can still make purchases as long as you do not require a shipping address, as that form only supports U.S.-based addresses.
In the meantime, you may use a Text Block to direct customers to reach out to you directly to arrange payment in another way.
We've made a test website here so you can see how it could look: https://icebox.onuniverse.com/shop/paypal
We plan to support other international currencies at a later time. Please let us know where you are located and what currency you use so that we can add you to our list by sending us a message in the app or emailing firstname.lastname@example.org.