It says here that it’s non-transferable and can only be used with your country’s currency. It’s not possible to add funds to the US side with an EURO balance card or buy products there with your Euro balance.
You can try buying products with a regular debit card instead, I believe that may work but you may incur possible banking fees for different currency purchases.
Inform at your bank if you want to make use of this feature.
Buying with a debit card works, it is how I pay for my US subscription. Once the banks have taken their currency conversion fees, a subscription (for my bank) works out £4 more expensive than a EU one.
I don’t know where you are, but in the UK there are credit cards that don’t charge fees for overseas currency purchases … I know because I have one and I presume maybe other countries have the same.