The answer is simple. Anywhere Visa & Mastercard are accepted online lol. However, sometimes VCCs don't work everywhere, like to pay a phone bill for example because they want a card issued locally and not a foreign Visa card. Amazon once blocked me for using a VCC
But do you think there could be more than that? like something about the card issuer. Saw a bunch of users asking ezzocard whether X accepts their card. I expected the same answer but what I got was how unsure they were about certain services that they haven't tried or haven't heard feedback from.