Hey there! Please refer to the FAQ:
The card selects which balance to use in the following order:
*The local currency of the merchant/ATM e.g. if you are in Spain, it will deduct funds from your Euro balance.
*Your base currency - i.e. if you used a UK address to sign-up, your base currency will be GBP.
*Your largest balance.
You need to have sufficient funds in one single balance in order to make a transaction. If you don’t have enough funds in the balance of the local currency, it will default to your next largest balance and so on.