At this moment, you can’t pay using more than one currency at the same time. You can only choose one currency, and it needs to have enough balance to make the payment.
For example, if you want to make a payment of 1000 pesos, but have a balance of 500 in ARS and 500 pesos in Bitcoin, the payment won't be concluded.
You'll need to have the total amount in the chosen currency, so 1000 pesos in ARS, or 1000 in a supported cryptocurrency.
If you don't have enough balance, you can always convert from one currency to another in the app before paying.
Learn more about converting your funds here (in Spanish):