If you are experiencing issues after setting up USD as the default currency within your account the next step is to check your “Payment Receiving Preferences”.
You can do this at the link below when logged into your Paypal account:
This specific setting has an impact on Adaptive Payments which JVZoo uses.
If this doesn't work you will need to get in contact with PayPal directly to have them take a look at your account settings.
View the tutorial to Set your currency to USD