Hope this helps:
Can the Vanilla Visa Gift Card Be Used to Shop Online?
The short answer is yes and no. Yes, because Vanilla Visa has information on their FAQs addressing the issue of using the card online. They do encourage card holders to use their mailing address when using the card online. They do not explicitly say that you cannot use the card online, but they do acknowledge that your personal information is not linked to the card. And that is where the problem lies. Since your personal information is not linked to the card, when the online merchant tries to verify the name and address you provide against the information on file with your gift card issuer (just like the do for credit cards), they are not able to match the information against your Vanilla Visa card, which leads to the card being rejected. I am not sure why Vanilla Visa will not come out and just tell their customers that. Some people buy these cards with the hope of using them online only to find out they cannot. That can be frustrating.