The virtual debit card is linked to your currency wallets. A payment made in any currency is deducted from the corresponding currency balance. E.g. if you make a payment in AUD at Subway in Australia, the card will deduct the amount from your AUD balance.
Yes, the card works for e-commerce, online merchants, in-app subscriptions, travel bookings, etc. You can use the same card details for both online checkouts or pay via Apple Pay / Google Pay.
There are no separate card usage fees for online or contactless payments made via POS. FX markup may apply when conversion is required (only when spending from a different currency wallet than the spend currency).