All balances held in the Sling Wallet and all transactions between Sling users and with Sling Link are conducted using USDC, a digital currency pegged to the US Dollar.
You can choose to display your Sling Wallet balance and your peer-to-peer transactions in any of a variety of global currencies. You can find the latest list of supported display currencies in the Sling App.
When you on-ramp or off-ramp funds with Sling you can do so using whatever your local, native currency is.