Your Sling Wallet always contains USDP, which is a stablecoin pegged to the US Dollar issued by Paxos Trust Company LLC.
For ease of use, the Sling Money app always displays this balance in USDP and a balance in a "primary currency" which you can change in your Settings. You can set this primary currency to almost any currency in the world.
We use constantly updated exchange rates to display the most accurate value of your USDP balance in your "primary currency" at all times. This means that the non-USDP currency balance displayed in your app may change from time to time as the exchange rate between the US Dollar and your primary currency change.
You can also change your primary currency at any time. For example, if you're travelling in Thailand you can update Sling Money to display your balance to you in Thai Baht. And then when you cross the border into Malaysia you can update your primary currency to Malaysian Ringitt.